Make getpid() use %d consistently for printing.

[postgresql] / src / backend / access / transam / xlog.c

/*-------------------------------------------------------------------------
 *
 * xlog.c
 *              PostgreSQL transaction log manager
 *
 *
 * Portions Copyright (c) 1996-2004, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.172 2004/10/09 02:46:40 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include <ctype.h>
#include <fcntl.h>
#include <signal.h>
#include <time.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/time.h>

#include "access/clog.h"
#include "access/subtrans.h"
#include "access/xact.h"
#include "access/xlog.h"
#include "access/xlog_internal.h"
#include "access/xlogutils.h"
#include "catalog/catversion.h"
#include "catalog/pg_control.h"
#include "miscadmin.h"
#include "postmaster/bgwriter.h"
#include "storage/bufpage.h"
#include "storage/fd.h"
#include "storage/lwlock.h"
#include "storage/pmsignal.h"
#include "storage/proc.h"
#include "storage/sinval.h"
#include "storage/spin.h"
#include "utils/builtins.h"
#include "utils/guc.h"
#include "utils/relcache.h"


/*
 * This chunk of hackery attempts to determine which file sync methods
 * are available on the current platform, and to choose an appropriate
 * default method.      We assume that fsync() is always available, and that
 * configure determined whether fdatasync() is.
 */
#define SYNC_METHOD_FSYNC               0
#define SYNC_METHOD_FDATASYNC   1
#define SYNC_METHOD_OPEN                2               /* used for both O_SYNC and
                                                                                 * O_DSYNC */

#if defined(O_SYNC)
#define OPEN_SYNC_FLAG     O_SYNC
#else
#if defined(O_FSYNC)
#define OPEN_SYNC_FLAG    O_FSYNC
#endif
#endif

#if defined(OPEN_SYNC_FLAG)
#if defined(O_DSYNC) && (O_DSYNC != OPEN_SYNC_FLAG)
#define OPEN_DATASYNC_FLAG        O_DSYNC
#endif
#endif

#if defined(OPEN_DATASYNC_FLAG)
#define DEFAULT_SYNC_METHOD_STR    "open_datasync"
#define DEFAULT_SYNC_METHOD                SYNC_METHOD_OPEN
#define DEFAULT_SYNC_FLAGBIT       OPEN_DATASYNC_FLAG
#else
#if defined(HAVE_FDATASYNC)
#define DEFAULT_SYNC_METHOD_STR   "fdatasync"
#define DEFAULT_SYNC_METHOD               SYNC_METHOD_FDATASYNC
#define DEFAULT_SYNC_FLAGBIT      0
#else
#define DEFAULT_SYNC_METHOD_STR   "fsync"
#define DEFAULT_SYNC_METHOD               SYNC_METHOD_FSYNC
#define DEFAULT_SYNC_FLAGBIT      0
#endif
#endif


/* User-settable parameters */
int                     CheckPointSegments = 3;
int                     XLOGbuffers = 8;
char       *XLogArchiveCommand = NULL;
char       *XLOG_sync_method = NULL;
const char      XLOG_sync_method_default[] = DEFAULT_SYNC_METHOD_STR;

#ifdef WAL_DEBUG
bool            XLOG_DEBUG = false;
#endif

/*
 * XLOGfileslop is used in the code as the allowed "fuzz" in the number of
 * preallocated XLOG segments --- we try to have at least XLOGfiles advance
 * segments but no more than XLOGfileslop segments.  This could
 * be made a separate GUC variable, but at present I think it's sufficient
 * to hardwire it as 2*CheckPointSegments+1.  Under normal conditions, a
 * checkpoint will free no more than 2*CheckPointSegments log segments, and
 * we want to recycle all of them; the +1 allows boundary cases to happen
 * without wasting a delete/create-segment cycle.
 */

#define XLOGfileslop    (2*CheckPointSegments + 1)


/* these are derived from XLOG_sync_method by assign_xlog_sync_method */
static int      sync_method = DEFAULT_SYNC_METHOD;
static int      open_sync_bit = DEFAULT_SYNC_FLAGBIT;

#define XLOG_SYNC_BIT  (enableFsync ? open_sync_bit : 0)

#define MinXLOGbuffers  4


/*
 * ThisTimeLineID will be same in all backends --- it identifies current
 * WAL timeline for the database system.
 */
TimeLineID      ThisTimeLineID = 0;

/* Are we doing recovery from XLOG? */
bool            InRecovery = false;

/* Are we recovering using offline XLOG archives? */
static bool InArchiveRecovery = false;

/* Was the last xlog file restored from archive, or local? */
static bool restoredFromArchive = false;

/* options taken from recovery.conf */
static char *recoveryRestoreCommand = NULL;
static bool recoveryTarget = false;
static bool recoveryTargetExact = false;
static bool recoveryTargetInclusive = true;
static TransactionId recoveryTargetXid;
static time_t recoveryTargetTime;

/* if recoveryStopsHere returns true, it saves actual stop xid/time here */
static TransactionId recoveryStopXid;
static time_t recoveryStopTime;
static bool recoveryStopAfter;

/* constraint set by read_backup_label */
static XLogRecPtr recoveryMinXlogOffset = {0, 0};

/*
 * During normal operation, the only timeline we care about is ThisTimeLineID.
 * During recovery, however, things are more complicated.  To simplify life
 * for rmgr code, we keep ThisTimeLineID set to the "current" timeline as we
 * scan through the WAL history (that is, it is the line that was active when
 * the currently-scanned WAL record was generated).  We also need these
 * timeline values:
 *
 * recoveryTargetTLI: the desired timeline that we want to end in.
 *
 * expectedTLIs: an integer list of recoveryTargetTLI and the TLIs of
 * its known parents, newest first (so recoveryTargetTLI is always the
 * first list member).  Only these TLIs are expected to be seen in the WAL
 * segments we read, and indeed only these TLIs will be considered as
 * candidate WAL files to open at all.
 *
 * curFileTLI: the TLI appearing in the name of the current input WAL file.
 * (This is not necessarily the same as ThisTimeLineID, because we could
 * be scanning data that was copied from an ancestor timeline when the current
 * file was created.)  During a sequential scan we do not allow this value
 * to decrease.
 */
static TimeLineID recoveryTargetTLI;
static List *expectedTLIs;
static TimeLineID curFileTLI;

/*
 * MyLastRecPtr points to the start of the last XLOG record inserted by the
 * current transaction.  If MyLastRecPtr.xrecoff == 0, then the current
 * xact hasn't yet inserted any transaction-controlled XLOG records.
 *
 * Note that XLOG records inserted outside transaction control are not
 * reflected into MyLastRecPtr.  They do, however, cause MyXactMadeXLogEntry
 * to be set true.      The latter can be used to test whether the current xact
 * made any loggable changes (including out-of-xact changes, such as
 * sequence updates).
 *
 * When we insert/update/delete a tuple in a temporary relation, we do not
 * make any XLOG record, since we don't care about recovering the state of
 * the temp rel after a crash.  However, we will still need to remember
 * whether our transaction committed or aborted in that case.  So, we must
 * set MyXactMadeTempRelUpdate true to indicate that the XID will be of
 * interest later.
 */
XLogRecPtr      MyLastRecPtr = {0, 0};

bool            MyXactMadeXLogEntry = false;

bool            MyXactMadeTempRelUpdate = false;

/*
 * ProcLastRecPtr points to the start of the last XLOG record inserted by the
 * current backend.  It is updated for all inserts, transaction-controlled
 * or not.      ProcLastRecEnd is similar but points to end+1 of last record.
 */
static XLogRecPtr ProcLastRecPtr = {0, 0};

XLogRecPtr      ProcLastRecEnd = {0, 0};

/*
 * RedoRecPtr is this backend's local copy of the REDO record pointer
 * (which is almost but not quite the same as a pointer to the most recent
 * CHECKPOINT record).  We update this from the shared-memory copy,
 * XLogCtl->Insert.RedoRecPtr, whenever we can safely do so (ie, when we
 * hold the Insert lock).  See XLogInsert for details.  We are also allowed
 * to update from XLogCtl->Insert.RedoRecPtr if we hold the info_lck;
 * see GetRedoRecPtr.  A freshly spawned backend obtains the value during
 * InitXLOGAccess.
 */
static XLogRecPtr RedoRecPtr;

/*----------
 * Shared-memory data structures for XLOG control
 *
 * LogwrtRqst indicates a byte position that we need to write and/or fsync
 * the log up to (all records before that point must be written or fsynced).
 * LogwrtResult indicates the byte positions we have already written/fsynced.
 * These structs are identical but are declared separately to indicate their
 * slightly different functions.
 *
 * We do a lot of pushups to minimize the amount of access to lockable
 * shared memory values.  There are actually three shared-memory copies of
 * LogwrtResult, plus one unshared copy in each backend.  Here's how it works:
 *              XLogCtl->LogwrtResult is protected by info_lck
 *              XLogCtl->Write.LogwrtResult is protected by WALWriteLock
 *              XLogCtl->Insert.LogwrtResult is protected by WALInsertLock
 * One must hold the associated lock to read or write any of these, but
 * of course no lock is needed to read/write the unshared LogwrtResult.
 *
 * XLogCtl->LogwrtResult and XLogCtl->Write.LogwrtResult are both "always
 * right", since both are updated by a write or flush operation before
 * it releases WALWriteLock.  The point of keeping XLogCtl->Write.LogwrtResult
 * is that it can be examined/modified by code that already holds WALWriteLock
 * without needing to grab info_lck as well.
 *
 * XLogCtl->Insert.LogwrtResult may lag behind the reality of the other two,
 * but is updated when convenient.      Again, it exists for the convenience of
 * code that is already holding WALInsertLock but not the other locks.
 *
 * The unshared LogwrtResult may lag behind any or all of these, and again
 * is updated when convenient.
 *
 * The request bookkeeping is simpler: there is a shared XLogCtl->LogwrtRqst
 * (protected by info_lck), but we don't need to cache any copies of it.
 *
 * Note that this all works because the request and result positions can only
 * advance forward, never back up, and so we can easily determine which of two
 * values is "more up to date".
 *
 * info_lck is only held long enough to read/update the protected variables,
 * so it's a plain spinlock.  The other locks are held longer (potentially
 * over I/O operations), so we use LWLocks for them.  These locks are:
 *
 * WALInsertLock: must be held to insert a record into the WAL buffers.
 *
 * WALWriteLock: must be held to write WAL buffers to disk (XLogWrite or
 * XLogFlush).
 *
 * ControlFileLock: must be held to read/update control file or create
 * new log file.
 *
 * CheckpointLock: must be held to do a checkpoint (ensures only one
 * checkpointer at a time; even though the postmaster won't launch
 * parallel checkpoint processes, we need this because manual checkpoints
 * could be launched simultaneously).
 *
 *----------
 */

typedef struct XLogwrtRqst
{
        XLogRecPtr      Write;                  /* last byte + 1 to write out */
        XLogRecPtr      Flush;                  /* last byte + 1 to flush */
} XLogwrtRqst;

typedef struct XLogwrtResult
{
        XLogRecPtr      Write;                  /* last byte + 1 written out */
        XLogRecPtr      Flush;                  /* last byte + 1 flushed */
} XLogwrtResult;

/*
 * Shared state data for XLogInsert.
 */
typedef struct XLogCtlInsert
{
        XLogwrtResult LogwrtResult; /* a recent value of LogwrtResult */
        XLogRecPtr      PrevRecord;             /* start of previously-inserted record */
        uint16          curridx;                /* current block index in cache */
        XLogPageHeader currpage;        /* points to header of block in cache */
        char       *currpos;            /* current insertion point in cache */
        XLogRecPtr      RedoRecPtr;             /* current redo point for insertions */
} XLogCtlInsert;

/*
 * Shared state data for XLogWrite/XLogFlush.
 */
typedef struct XLogCtlWrite
{
        XLogwrtResult LogwrtResult; /* current value of LogwrtResult */
        uint16          curridx;                /* cache index of next block to write */
} XLogCtlWrite;

/*
 * Total shared-memory state for XLOG.
 */
typedef struct XLogCtlData
{
        /* Protected by WALInsertLock: */
        XLogCtlInsert Insert;
        /* Protected by info_lck: */
        XLogwrtRqst LogwrtRqst;
        XLogwrtResult LogwrtResult;
        /* Protected by WALWriteLock: */
        XLogCtlWrite Write;

        /*
         * These values do not change after startup, although the pointed-to
         * pages and xlblocks values certainly do.      Permission to read/write
         * the pages and xlblocks values depends on WALInsertLock and
         * WALWriteLock.
         */
        char       *pages;                      /* buffers for unwritten XLOG pages */
        XLogRecPtr *xlblocks;           /* 1st byte ptr-s + BLCKSZ */
        uint32          XLogCacheByte;  /* # bytes in xlog buffers */
        uint32          XLogCacheBlck;  /* highest allocated xlog buffer index */
        TimeLineID      ThisTimeLineID;

        slock_t         info_lck;               /* locks shared LogwrtRqst/LogwrtResult */
} XLogCtlData;

static XLogCtlData *XLogCtl = NULL;

/*
 * We maintain an image of pg_control in shared memory.
 */
static ControlFileData *ControlFile = NULL;

/*
 * Macros for managing XLogInsert state.  In most cases, the calling routine
 * has local copies of XLogCtl->Insert and/or XLogCtl->Insert->curridx,
 * so these are passed as parameters instead of being fetched via XLogCtl.
 */

/* Free space remaining in the current xlog page buffer */
#define INSERT_FREESPACE(Insert)  \
        (BLCKSZ - ((Insert)->currpos - (char *) (Insert)->currpage))

/* Construct XLogRecPtr value for current insertion point */
#define INSERT_RECPTR(recptr,Insert,curridx)  \
        ( \
          (recptr).xlogid = XLogCtl->xlblocks[curridx].xlogid, \
          (recptr).xrecoff = \
                XLogCtl->xlblocks[curridx].xrecoff - INSERT_FREESPACE(Insert) \
        )

#define PrevBufIdx(idx)         \
                (((idx) == 0) ? XLogCtl->XLogCacheBlck : ((idx) - 1))

#define NextBufIdx(idx)         \
                (((idx) == XLogCtl->XLogCacheBlck) ? 0 : ((idx) + 1))


/* File path names */
char            XLogDir[MAXPGPATH];
static char ControlFilePath[MAXPGPATH];

/*
 * Private, possibly out-of-date copy of shared LogwrtResult.
 * See discussion above.
 */
static XLogwrtResult LogwrtResult = {{0, 0}, {0, 0}};

/*
 * openLogFile is -1 or a kernel FD for an open log file segment.
 * When it's open, openLogOff is the current seek offset in the file.
 * openLogId/openLogSeg identify the segment.  These variables are only
 * used to write the XLOG, and so will normally refer to the active segment.
 */
static int      openLogFile = -1;
static uint32 openLogId = 0;
static uint32 openLogSeg = 0;
static uint32 openLogOff = 0;

/*
 * These variables are used similarly to the ones above, but for reading
 * the XLOG.  Note, however, that readOff generally represents the offset
 * of the page just read, not the seek position of the FD itself, which
 * will be just past that page.
 */
static int      readFile = -1;
static uint32 readId = 0;
static uint32 readSeg = 0;
static uint32 readOff = 0;

/* Buffer for currently read page (BLCKSZ bytes) */
static char *readBuf = NULL;

/* Buffer for current ReadRecord result (expandable) */
static char *readRecordBuf = NULL;
static uint32 readRecordBufSize = 0;

/* State information for XLOG reading */
static XLogRecPtr ReadRecPtr;
static XLogRecPtr EndRecPtr;
static XLogRecord *nextRecord = NULL;
static TimeLineID lastPageTLI = 0;

static bool InRedo = false;


static void XLogArchiveNotify(const char *xlog);
static void XLogArchiveNotifySeg(uint32 log, uint32 seg);
static bool XLogArchiveIsDone(const char *xlog);
static void XLogArchiveCleanup(const char *xlog);
static void readRecoveryCommandFile(void);
static void exitArchiveRecovery(TimeLineID endTLI,
                                        uint32 endLogId, uint32 endLogSeg);
static bool recoveryStopsHere(XLogRecord *record, bool *includeThis);

static bool AdvanceXLInsertBuffer(void);
static void XLogWrite(XLogwrtRqst WriteRqst);
static int XLogFileInit(uint32 log, uint32 seg,
                         bool *use_existent, bool use_lock);
static bool InstallXLogFileSegment(uint32 log, uint32 seg, char *tmppath,
                                           bool find_free, int max_advance,
                                           bool use_lock);
static int      XLogFileOpen(uint32 log, uint32 seg);
static int      XLogFileRead(uint32 log, uint32 seg, int emode);
static bool RestoreArchivedFile(char *path, const char *xlogfname,
                                        const char *recovername, off_t expectedSize);
static void PreallocXlogFiles(XLogRecPtr endptr);
static void MoveOfflineLogs(uint32 log, uint32 seg, XLogRecPtr endptr);
static XLogRecord *ReadRecord(XLogRecPtr *RecPtr, int emode);
static bool ValidXLOGHeader(XLogPageHeader hdr, int emode);
static XLogRecord *ReadCheckpointRecord(XLogRecPtr RecPtr, int whichChkpt);
static List *readTimeLineHistory(TimeLineID targetTLI);
static bool existsTimeLineHistory(TimeLineID probeTLI);
static TimeLineID findNewestTimeLine(TimeLineID startTLI);
static void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI,
                                         TimeLineID endTLI,
                                         uint32 endLogId, uint32 endLogSeg);
static void WriteControlFile(void);
static void ReadControlFile(void);
static char *str_time(time_t tnow);
static void issue_xlog_fsync(void);

#ifdef WAL_DEBUG
static void xlog_outrec(char *buf, XLogRecord *record);
#endif
static bool read_backup_label(XLogRecPtr *checkPointLoc);
static void remove_backup_label(void);


/*
 * Insert an XLOG record having the specified RMID and info bytes,
 * with the body of the record being the data chunk(s) described by
 * the rdata list (see xlog.h for notes about rdata).
 *
 * Returns XLOG pointer to end of record (beginning of next record).
 * This can be used as LSN for data pages affected by the logged action.
 * (LSN is the XLOG point up to which the XLOG must be flushed to disk
 * before the data page can be written out.  This implements the basic
 * WAL rule "write the log before the data".)
 *
 * NB: this routine feels free to scribble on the XLogRecData structs,
 * though not on the data they reference.  This is OK since the XLogRecData
 * structs are always just temporaries in the calling code.
 */
XLogRecPtr
XLogInsert(RmgrId rmid, uint8 info, XLogRecData *rdata)
{
        XLogCtlInsert *Insert = &XLogCtl->Insert;
        XLogRecord *record;
        XLogContRecord *contrecord;
        XLogRecPtr      RecPtr;
        XLogRecPtr      WriteRqst;
        uint32          freespace;
        uint16          curridx;
        XLogRecData *rdt;
        Buffer          dtbuf[XLR_MAX_BKP_BLOCKS];
        bool            dtbuf_bkp[XLR_MAX_BKP_BLOCKS];
        BkpBlock        dtbuf_xlg[XLR_MAX_BKP_BLOCKS];
        XLogRecPtr      dtbuf_lsn[XLR_MAX_BKP_BLOCKS];
        XLogRecData dtbuf_rdt[2 * XLR_MAX_BKP_BLOCKS];
        crc64           rdata_crc;
        uint32          len,
                                write_len;
        unsigned        i;
        XLogwrtRqst LogwrtRqst;
        bool            updrqst;
        bool            no_tran = (rmid == RM_XLOG_ID) ? true : false;

        if (info & XLR_INFO_MASK)
        {
                if ((info & XLR_INFO_MASK) != XLOG_NO_TRAN)
                        elog(PANIC, "invalid xlog info mask %02X", (info & XLR_INFO_MASK));
                no_tran = true;
                info &= ~XLR_INFO_MASK;
        }

        /*
         * In bootstrap mode, we don't actually log anything but XLOG
         * resources; return a phony record pointer.
         */
        if (IsBootstrapProcessingMode() && rmid != RM_XLOG_ID)
        {
                RecPtr.xlogid = 0;
                RecPtr.xrecoff = SizeOfXLogLongPHD;             /* start of 1st chkpt
                                                                                                 * record */
                return (RecPtr);
        }

        /*
         * Here we scan the rdata list, determine which buffers must be backed
         * up, and compute the CRC values for the data.  Note that the record
         * header isn't added into the CRC yet since we don't know the final
         * length or info bits quite yet.
         *
         * We may have to loop back to here if a race condition is detected
         * below. We could prevent the race by doing all this work while
         * holding the insert lock, but it seems better to avoid doing CRC
         * calculations while holding the lock.  This means we have to be
         * careful about modifying the rdata list until we know we aren't
         * going to loop back again.  The only change we allow ourselves to
         * make earlier is to set rdt->data = NULL in list items we have
         * decided we will have to back up the whole buffer for.  This is OK
         * because we will certainly decide the same thing again for those
         * items if we do it over; doing it here saves an extra pass over the
         * list later.
         */
begin:;
        for (i = 0; i < XLR_MAX_BKP_BLOCKS; i++)
        {
                dtbuf[i] = InvalidBuffer;
                dtbuf_bkp[i] = false;
        }

        INIT_CRC64(rdata_crc);
        len = 0;
        for (rdt = rdata;;)
        {
                if (rdt->buffer == InvalidBuffer)
                {
                        /* Simple data, just include it */
                        len += rdt->len;
                        COMP_CRC64(rdata_crc, rdt->data, rdt->len);
                }
                else
                {
                        /* Find info for buffer */
                        for (i = 0; i < XLR_MAX_BKP_BLOCKS; i++)
                        {
                                if (rdt->buffer == dtbuf[i])
                                {
                                        /* Buffer already referenced by earlier list item */
                                        if (dtbuf_bkp[i])
                                                rdt->data = NULL;
                                        else if (rdt->data)
                                        {
                                                len += rdt->len;
                                                COMP_CRC64(rdata_crc, rdt->data, rdt->len);
                                        }
                                        break;
                                }
                                if (dtbuf[i] == InvalidBuffer)
                                {
                                        /* OK, put it in this slot */
                                        dtbuf[i] = rdt->buffer;

                                        /*
                                         * XXX We assume page LSN is first data on page
                                         */
                                        dtbuf_lsn[i] = *((XLogRecPtr *) BufferGetBlock(rdt->buffer));
                                        if (XLByteLE(dtbuf_lsn[i], RedoRecPtr))
                                        {
                                                crc64           dtcrc;

                                                dtbuf_bkp[i] = true;
                                                rdt->data = NULL;
                                                INIT_CRC64(dtcrc);
                                                COMP_CRC64(dtcrc,
                                                                   BufferGetBlock(dtbuf[i]),
                                                                   BLCKSZ);
                                                dtbuf_xlg[i].node = BufferGetFileNode(dtbuf[i]);
                                                dtbuf_xlg[i].block = BufferGetBlockNumber(dtbuf[i]);
                                                COMP_CRC64(dtcrc,
                                                                (char *) &(dtbuf_xlg[i]) + sizeof(crc64),
                                                                   sizeof(BkpBlock) - sizeof(crc64));
                                                FIN_CRC64(dtcrc);
                                                dtbuf_xlg[i].crc = dtcrc;
                                        }
                                        else if (rdt->data)
                                        {
                                                len += rdt->len;
                                                COMP_CRC64(rdata_crc, rdt->data, rdt->len);
                                        }
                                        break;
                                }
                        }
                        if (i >= XLR_MAX_BKP_BLOCKS)
                                elog(PANIC, "can backup at most %d blocks per xlog record",
                                         XLR_MAX_BKP_BLOCKS);
                }
                /* Break out of loop when rdt points to last list item */
                if (rdt->next == NULL)
                        break;
                rdt = rdt->next;
        }

        /*
         * NOTE: the test for len == 0 here is somewhat fishy, since in theory
         * all of the rmgr data might have been suppressed in favor of backup
         * blocks.      Currently, all callers of XLogInsert provide at least some
         * not-in-a-buffer data and so len == 0 should never happen, but that
         * may not be true forever.  If you need to remove the len == 0 check,
         * also remove the check for xl_len == 0 in ReadRecord, below.
         */
        if (len == 0)
                elog(PANIC, "invalid xlog record length %u", len);

        START_CRIT_SECTION();

        /* update LogwrtResult before doing cache fill check */
        {
                /* use volatile pointer to prevent code rearrangement */
                volatile XLogCtlData *xlogctl = XLogCtl;

                SpinLockAcquire_NoHoldoff(&xlogctl->info_lck);
                LogwrtRqst = xlogctl->LogwrtRqst;
                LogwrtResult = xlogctl->LogwrtResult;
                SpinLockRelease_NoHoldoff(&xlogctl->info_lck);
        }

        /*
         * If cache is half filled then try to acquire write lock and do
         * XLogWrite. Ignore any fractional blocks in performing this check.
         */
        LogwrtRqst.Write.xrecoff -= LogwrtRqst.Write.xrecoff % BLCKSZ;
        if (LogwrtRqst.Write.xlogid != LogwrtResult.Write.xlogid ||
                (LogwrtRqst.Write.xrecoff >= LogwrtResult.Write.xrecoff +
                 XLogCtl->XLogCacheByte / 2))
        {
                if (LWLockConditionalAcquire(WALWriteLock, LW_EXCLUSIVE))
                {
                        LogwrtResult = XLogCtl->Write.LogwrtResult;
                        if (XLByteLT(LogwrtResult.Write, LogwrtRqst.Write))
                                XLogWrite(LogwrtRqst);
                        LWLockRelease(WALWriteLock);
                }
        }

        /* Now wait to get insert lock */
        LWLockAcquire(WALInsertLock, LW_EXCLUSIVE);

        /*
         * Check to see if my RedoRecPtr is out of date.  If so, may have to
         * go back and recompute everything.  This can only happen just after
         * a checkpoint, so it's better to be slow in this case and fast
         * otherwise.
         */
        if (!XLByteEQ(RedoRecPtr, Insert->RedoRecPtr))
        {
                Assert(XLByteLT(RedoRecPtr, Insert->RedoRecPtr));
                RedoRecPtr = Insert->RedoRecPtr;

                for (i = 0; i < XLR_MAX_BKP_BLOCKS; i++)
                {
                        if (dtbuf[i] == InvalidBuffer)
                                continue;
                        if (dtbuf_bkp[i] == false &&
                                XLByteLE(dtbuf_lsn[i], RedoRecPtr))
                        {
                                /*
                                 * Oops, this buffer now needs to be backed up, but we
                                 * didn't think so above.  Start over.
                                 */
                                LWLockRelease(WALInsertLock);
                                END_CRIT_SECTION();
                                goto begin;
                        }
                }
        }

        /*
         * Make additional rdata list entries for the backup blocks, so that
         * we don't need to special-case them in the write loop.  Note that we
         * have now irrevocably changed the input rdata list.  At the exit of
         * this loop, write_len includes the backup block data.
         *
         * Also set the appropriate info bits to show which buffers were backed
         * up.  The i'th XLR_SET_BKP_BLOCK bit corresponds to the i'th
         * distinct buffer value (ignoring InvalidBuffer) appearing in the
         * rdata list.
         */
        write_len = len;
        for (i = 0; i < XLR_MAX_BKP_BLOCKS; i++)
        {
                if (dtbuf[i] == InvalidBuffer || !(dtbuf_bkp[i]))
                        continue;

                info |= XLR_SET_BKP_BLOCK(i);

                rdt->next = &(dtbuf_rdt[2 * i]);

                dtbuf_rdt[2 * i].data = (char *) &(dtbuf_xlg[i]);
                dtbuf_rdt[2 * i].len = sizeof(BkpBlock);
                write_len += sizeof(BkpBlock);

                rdt = dtbuf_rdt[2 * i].next = &(dtbuf_rdt[2 * i + 1]);

                dtbuf_rdt[2 * i + 1].data = (char *) BufferGetBlock(dtbuf[i]);
                dtbuf_rdt[2 * i + 1].len = BLCKSZ;
                write_len += BLCKSZ;
                dtbuf_rdt[2 * i + 1].next = NULL;
        }

        /*
         * If there isn't enough space on the current XLOG page for a record
         * header, advance to the next page (leaving the unused space as
         * zeroes).
         */
        updrqst = false;
        freespace = INSERT_FREESPACE(Insert);
        if (freespace < SizeOfXLogRecord)
        {
                updrqst = AdvanceXLInsertBuffer();
                freespace = INSERT_FREESPACE(Insert);
        }

        curridx = Insert->curridx;
        record = (XLogRecord *) Insert->currpos;

        /* Insert record header */

        record->xl_prev = Insert->PrevRecord;
        record->xl_xid = GetCurrentTransactionIdIfAny();
        record->xl_len = len;           /* doesn't include backup blocks */
        record->xl_info = info;
        record->xl_rmid = rmid;

        /* Now we can finish computing the main CRC */
        COMP_CRC64(rdata_crc, (char *) record + sizeof(crc64),
                           SizeOfXLogRecord - sizeof(crc64));
        FIN_CRC64(rdata_crc);
        record->xl_crc = rdata_crc;

        /* Compute record's XLOG location */
        INSERT_RECPTR(RecPtr, Insert, curridx);

        /* If first XLOG record of transaction, save it in PGPROC array */
        if (MyLastRecPtr.xrecoff == 0 && !no_tran)
        {
                /*
                 * We do not acquire SInvalLock here because of possible deadlock.
                 * Anyone who wants to inspect other procs' logRec must acquire
                 * WALInsertLock, instead.      A better solution would be a per-PROC
                 * spinlock, but no time for that before 7.2 --- tgl 12/19/01.
                 */
                MyProc->logRec = RecPtr;
        }

#ifdef WAL_DEBUG
        if (XLOG_DEBUG)
        {
                char            buf[8192];

                sprintf(buf, "INSERT @ %X/%X: ", RecPtr.xlogid, RecPtr.xrecoff);
                xlog_outrec(buf, record);
                if (rdata->data != NULL)
                {
                        strcat(buf, " - ");
                        RmgrTable[record->xl_rmid].rm_desc(buf, record->xl_info, rdata->data);
                }
                elog(LOG, "%s", buf);
        }
#endif

        /* Record begin of record in appropriate places */
        if (!no_tran)
                MyLastRecPtr = RecPtr;
        ProcLastRecPtr = RecPtr;
        Insert->PrevRecord = RecPtr;
        MyXactMadeXLogEntry = true;

        Insert->currpos += SizeOfXLogRecord;
        freespace -= SizeOfXLogRecord;

        /*
         * Append the data, including backup blocks if any
         */
        while (write_len)
        {
                while (rdata->data == NULL)
                        rdata = rdata->next;

                if (freespace > 0)
                {
                        if (rdata->len > freespace)
                        {
                                memcpy(Insert->currpos, rdata->data, freespace);
                                rdata->data += freespace;
                                rdata->len -= freespace;
                                write_len -= freespace;
                        }
                        else
                        {
                                memcpy(Insert->currpos, rdata->data, rdata->len);
                                freespace -= rdata->len;
                                write_len -= rdata->len;
                                Insert->currpos += rdata->len;
                                rdata = rdata->next;
                                continue;
                        }
                }

                /* Use next buffer */
                updrqst = AdvanceXLInsertBuffer();
                curridx = Insert->curridx;
                /* Insert cont-record header */
                Insert->currpage->xlp_info |= XLP_FIRST_IS_CONTRECORD;
                contrecord = (XLogContRecord *) Insert->currpos;
                contrecord->xl_rem_len = write_len;
                Insert->currpos += SizeOfXLogContRecord;
                freespace = INSERT_FREESPACE(Insert);
        }

        /* Ensure next record will be properly aligned */
        Insert->currpos = (char *) Insert->currpage +
                MAXALIGN(Insert->currpos - (char *) Insert->currpage);
        freespace = INSERT_FREESPACE(Insert);

        /*
         * The recptr I return is the beginning of the *next* record. This
         * will be stored as LSN for changed data pages...
         */
        INSERT_RECPTR(RecPtr, Insert, curridx);

        /* Need to update shared LogwrtRqst if some block was filled up */
        if (freespace < SizeOfXLogRecord)
                updrqst = true;                 /* curridx is filled and available for
                                                                 * writing out */
        else
                curridx = PrevBufIdx(curridx);
        WriteRqst = XLogCtl->xlblocks[curridx];

        LWLockRelease(WALInsertLock);

        if (updrqst)
        {
                /* use volatile pointer to prevent code rearrangement */
                volatile XLogCtlData *xlogctl = XLogCtl;

                SpinLockAcquire_NoHoldoff(&xlogctl->info_lck);
                /* advance global request to include new block(s) */
                if (XLByteLT(xlogctl->LogwrtRqst.Write, WriteRqst))
                        xlogctl->LogwrtRqst.Write = WriteRqst;
                /* update local result copy while I have the chance */
                LogwrtResult = xlogctl->LogwrtResult;
                SpinLockRelease_NoHoldoff(&xlogctl->info_lck);
        }

        ProcLastRecEnd = RecPtr;

        END_CRIT_SECTION();

        return (RecPtr);
}

/*
 * XLogArchiveNotify
 *
 * Create an archive notification file
 *
 * The name of the notification file is the message that will be picked up
 * by the archiver, e.g. we write 0000000100000001000000C6.ready
 * and the archiver then knows to archive XLogDir/0000000100000001000000C6,
 * then when complete, rename it to 0000000100000001000000C6.done
 */
static void
XLogArchiveNotify(const char *xlog)
{
        char            archiveStatusPath[MAXPGPATH];
        FILE       *fd;

        /* insert an otherwise empty file called <XLOG>.ready */
        StatusFilePath(archiveStatusPath, xlog, ".ready");
        fd = AllocateFile(archiveStatusPath, "w");
        if (fd == NULL)
        {
                ereport(LOG,
                                (errcode_for_file_access(),
                                 errmsg("could not create archive status file \"%s\": %m",
                                                archiveStatusPath)));
                return;
        }
        if (FreeFile(fd))
        {
                ereport(LOG,
                                (errcode_for_file_access(),
                                 errmsg("could not write archive status file \"%s\": %m",
                                                archiveStatusPath)));
                return;
        }

        /* Notify archiver that it's got something to do */
        if (IsUnderPostmaster)
                SendPostmasterSignal(PMSIGNAL_WAKEN_ARCHIVER);
}

/*
 * Convenience routine to notify using log/seg representation of filename
 */
static void
XLogArchiveNotifySeg(uint32 log, uint32 seg)
{
        char            xlog[MAXFNAMELEN];

        XLogFileName(xlog, ThisTimeLineID, log, seg);
        XLogArchiveNotify(xlog);
}

/*
 * XLogArchiveIsDone
 *
 * Checks for a ".done" archive notification file.      This is called when we
 * are ready to delete or recycle an old XLOG segment file.  If it is okay
 * to delete it then return true.
 *
 * If <XLOG>.done exists, then return true; else if <XLOG>.ready exists,
 * then return false; else create <XLOG>.ready and return false.  The
 * last case covers the possibility that the original attempt to create
 * <XLOG>.ready failed.
 */
static bool
XLogArchiveIsDone(const char *xlog)
{
        char            archiveStatusPath[MAXPGPATH];
        struct stat stat_buf;

        /* First check for .done --- this is the expected case */
        StatusFilePath(archiveStatusPath, xlog, ".done");
        if (stat(archiveStatusPath, &stat_buf) == 0)
                return true;

        /* check for .ready --- this means archiver is still busy with it */
        StatusFilePath(archiveStatusPath, xlog, ".ready");
        if (stat(archiveStatusPath, &stat_buf) == 0)
                return false;

        /* Race condition --- maybe archiver just finished, so recheck */
        StatusFilePath(archiveStatusPath, xlog, ".done");
        if (stat(archiveStatusPath, &stat_buf) == 0)
                return true;

        /* Retry creation of the .ready file */
        XLogArchiveNotify(xlog);
        return false;
}

/*
 * XLogArchiveCleanup
 *
 * Cleanup archive notification file(s) for a particular xlog segment
 */
static void
XLogArchiveCleanup(const char *xlog)
{
        char            archiveStatusPath[MAXPGPATH];

        /* Remove the .done file */
        StatusFilePath(archiveStatusPath, xlog, ".done");
        unlink(archiveStatusPath);
        /* should we complain about failure? */

        /* Remove the .ready file if present --- normally it shouldn't be */
        StatusFilePath(archiveStatusPath, xlog, ".ready");
        unlink(archiveStatusPath);
        /* should we complain about failure? */
}

/*
 * Advance the Insert state to the next buffer page, writing out the next
 * buffer if it still contains unwritten data.
 *
 * The global LogwrtRqst.Write pointer needs to be advanced to include the
 * just-filled page.  If we can do this for free (without an extra lock),
 * we do so here.  Otherwise the caller must do it.  We return TRUE if the
 * request update still needs to be done, FALSE if we did it internally.
 *
 * Must be called with WALInsertLock held.
 */
static bool
AdvanceXLInsertBuffer(void)
{
        XLogCtlInsert *Insert = &XLogCtl->Insert;
        XLogCtlWrite *Write = &XLogCtl->Write;
        uint16          nextidx = NextBufIdx(Insert->curridx);
        bool            update_needed = true;
        XLogRecPtr      OldPageRqstPtr;
        XLogwrtRqst WriteRqst;
        XLogRecPtr      NewPageEndPtr;
        XLogPageHeader NewPage;

        /* Use Insert->LogwrtResult copy if it's more fresh */
        if (XLByteLT(LogwrtResult.Write, Insert->LogwrtResult.Write))
                LogwrtResult = Insert->LogwrtResult;

        /*
         * Get ending-offset of the buffer page we need to replace (this may
         * be zero if the buffer hasn't been used yet).  Fall through if it's
         * already written out.
         */
        OldPageRqstPtr = XLogCtl->xlblocks[nextidx];
        if (!XLByteLE(OldPageRqstPtr, LogwrtResult.Write))
        {
                /* nope, got work to do... */
                XLogRecPtr      FinishedPageRqstPtr;

                FinishedPageRqstPtr = XLogCtl->xlblocks[Insert->curridx];

                /* Before waiting, get info_lck and update LogwrtResult */
                {
                        /* use volatile pointer to prevent code rearrangement */
                        volatile XLogCtlData *xlogctl = XLogCtl;

                        SpinLockAcquire_NoHoldoff(&xlogctl->info_lck);
                        if (XLByteLT(xlogctl->LogwrtRqst.Write, FinishedPageRqstPtr))
                                xlogctl->LogwrtRqst.Write = FinishedPageRqstPtr;
                        LogwrtResult = xlogctl->LogwrtResult;
                        SpinLockRelease_NoHoldoff(&xlogctl->info_lck);
                }

                update_needed = false;  /* Did the shared-request update */

                if (XLByteLE(OldPageRqstPtr, LogwrtResult.Write))
                {
                        /* OK, someone wrote it already */
                        Insert->LogwrtResult = LogwrtResult;
                }
                else
                {
                        /* Must acquire write lock */
                        LWLockAcquire(WALWriteLock, LW_EXCLUSIVE);
                        LogwrtResult = Write->LogwrtResult;
                        if (XLByteLE(OldPageRqstPtr, LogwrtResult.Write))
                        {
                                /* OK, someone wrote it already */
                                LWLockRelease(WALWriteLock);
                                Insert->LogwrtResult = LogwrtResult;
                        }
                        else
                        {
                                /*
                                 * Have to write buffers while holding insert lock. This
                                 * is not good, so only write as much as we absolutely
                                 * must.
                                 */
                                WriteRqst.Write = OldPageRqstPtr;
                                WriteRqst.Flush.xlogid = 0;
                                WriteRqst.Flush.xrecoff = 0;
                                XLogWrite(WriteRqst);
                                LWLockRelease(WALWriteLock);
                                Insert->LogwrtResult = LogwrtResult;
                        }
                }
        }

        /*
         * Now the next buffer slot is free and we can set it up to be the
         * next output page.
         */
        NewPageEndPtr = XLogCtl->xlblocks[Insert->curridx];
        if (NewPageEndPtr.xrecoff >= XLogFileSize)
        {
                /* crossing a logid boundary */
                NewPageEndPtr.xlogid += 1;
                NewPageEndPtr.xrecoff = BLCKSZ;
        }
        else
                NewPageEndPtr.xrecoff += BLCKSZ;
        XLogCtl->xlblocks[nextidx] = NewPageEndPtr;
        NewPage = (XLogPageHeader) (XLogCtl->pages + nextidx * BLCKSZ);
        Insert->curridx = nextidx;
        Insert->currpage = NewPage;
        Insert->currpos = ((char *) NewPage) + SizeOfXLogShortPHD;

        /*
         * Be sure to re-zero the buffer so that bytes beyond what we've
         * written will look like zeroes and not valid XLOG records...
         */
        MemSet((char *) NewPage, 0, BLCKSZ);

        /*
         * Fill the new page's header
         */
        NewPage->xlp_magic = XLOG_PAGE_MAGIC;
        /* NewPage->xlp_info = 0; */    /* done by memset */
        NewPage->xlp_tli = ThisTimeLineID;
        NewPage->xlp_pageaddr.xlogid = NewPageEndPtr.xlogid;
        NewPage->xlp_pageaddr.xrecoff = NewPageEndPtr.xrecoff - BLCKSZ;

        /*
         * If first page of an XLOG segment file, make it a long header.
         */
        if ((NewPage->xlp_pageaddr.xrecoff % XLogSegSize) == 0)
        {
                XLogLongPageHeader NewLongPage = (XLogLongPageHeader) NewPage;

                NewLongPage->xlp_sysid = ControlFile->system_identifier;
                NewLongPage->xlp_seg_size = XLogSegSize;
                NewPage->xlp_info |= XLP_LONG_HEADER;
                Insert->currpos = ((char *) NewPage) + SizeOfXLogLongPHD;
        }

        return update_needed;
}

/*
 * Write and/or fsync the log at least as far as WriteRqst indicates.
 *
 * Must be called with WALWriteLock held.
 */
static void
XLogWrite(XLogwrtRqst WriteRqst)
{
        XLogCtlWrite *Write = &XLogCtl->Write;
        char       *from;
        bool            ispartialpage;
        bool            use_existent;

        /*
         * Update local LogwrtResult (caller probably did this already,
         * but...)
         */
        LogwrtResult = Write->LogwrtResult;

        while (XLByteLT(LogwrtResult.Write, WriteRqst.Write))
        {
                /*
                 * Make sure we're not ahead of the insert process.  This could
                 * happen if we're passed a bogus WriteRqst.Write that is past the
                 * end of the last page that's been initialized by
                 * AdvanceXLInsertBuffer.
                 */
                if (!XLByteLT(LogwrtResult.Write, XLogCtl->xlblocks[Write->curridx]))
                        elog(PANIC, "xlog write request %X/%X is past end of log %X/%X",
                                 LogwrtResult.Write.xlogid, LogwrtResult.Write.xrecoff,
                                 XLogCtl->xlblocks[Write->curridx].xlogid,
                                 XLogCtl->xlblocks[Write->curridx].xrecoff);

                /* Advance LogwrtResult.Write to end of current buffer page */
                LogwrtResult.Write = XLogCtl->xlblocks[Write->curridx];
                ispartialpage = XLByteLT(WriteRqst.Write, LogwrtResult.Write);

                if (!XLByteInPrevSeg(LogwrtResult.Write, openLogId, openLogSeg))
                {
                        /*
                         * Switch to new logfile segment.
                         */
                        if (openLogFile >= 0)
                        {
                                if (close(openLogFile))
                                        ereport(PANIC,
                                                        (errcode_for_file_access(),
                                        errmsg("could not close log file %u, segment %u: %m",
                                                   openLogId, openLogSeg)));
                                openLogFile = -1;
                        }
                        XLByteToPrevSeg(LogwrtResult.Write, openLogId, openLogSeg);

                        /* create/use new log file */
                        use_existent = true;
                        openLogFile = XLogFileInit(openLogId, openLogSeg,
                                                                           &use_existent, true);
                        openLogOff = 0;

                        /* update pg_control, unless someone else already did */
                        LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
                        if (ControlFile->logId < openLogId ||
                                (ControlFile->logId == openLogId &&
                                 ControlFile->logSeg < openLogSeg + 1))
                        {
                                ControlFile->logId = openLogId;
                                ControlFile->logSeg = openLogSeg + 1;
                                ControlFile->time = time(NULL);
                                UpdateControlFile();

                                /*
                                 * Signal postmaster to start a checkpoint if it's been
                                 * too long since the last one.  (We look at local copy of
                                 * RedoRecPtr which might be a little out of date, but
                                 * should be close enough for this purpose.)
                                 */
                                if (IsUnderPostmaster &&
                                        (openLogId != RedoRecPtr.xlogid ||
                                         openLogSeg >= (RedoRecPtr.xrecoff / XLogSegSize) +
                                         (uint32) CheckPointSegments))
                                {
#ifdef WAL_DEBUG
                                        if (XLOG_DEBUG)
                                                elog(LOG, "time for a checkpoint, signaling bgwriter");
#endif
                                        RequestCheckpoint(false);
                                }
                        }
                        LWLockRelease(ControlFileLock);
                }

                if (openLogFile < 0)
                {
                        XLByteToPrevSeg(LogwrtResult.Write, openLogId, openLogSeg);
                        openLogFile = XLogFileOpen(openLogId, openLogSeg);
                        openLogOff = 0;
                }

                /* Need to seek in the file? */
                if (openLogOff != (LogwrtResult.Write.xrecoff - BLCKSZ) % XLogSegSize)
                {
                        openLogOff = (LogwrtResult.Write.xrecoff - BLCKSZ) % XLogSegSize;
                        if (lseek(openLogFile, (off_t) openLogOff, SEEK_SET) < 0)
                                ereport(PANIC,
                                                (errcode_for_file_access(),
                                                 errmsg("could not seek in log file %u, segment %u to offset %u: %m",
                                                                openLogId, openLogSeg, openLogOff)));
                }

                /* OK to write the page */
                from = XLogCtl->pages + Write->curridx * BLCKSZ;
                errno = 0;
                if (write(openLogFile, from, BLCKSZ) != BLCKSZ)
                {
                        /* if write didn't set errno, assume problem is no disk space */
                        if (errno == 0)
                                errno = ENOSPC;
                        ereport(PANIC,
                                        (errcode_for_file_access(),
                                         errmsg("could not write to log file %u, segment %u at offset %u: %m",
                                                        openLogId, openLogSeg, openLogOff)));
                }
                openLogOff += BLCKSZ;

                /*
                 * If we just wrote the whole last page of a logfile segment,
                 * fsync the segment immediately.  This avoids having to go back
                 * and re-open prior segments when an fsync request comes along
                 * later. Doing it here ensures that one and only one backend will
                 * perform this fsync.
                 *
                 * This is also the right place to notify the Archiver that the
                 * segment is ready to copy to archival storage.
                 */
                if (openLogOff >= XLogSegSize && !ispartialpage)
                {
                        issue_xlog_fsync();
                        LogwrtResult.Flush = LogwrtResult.Write;        /* end of current page */

                        if (XLogArchivingActive())
                                XLogArchiveNotifySeg(openLogId, openLogSeg);
                }

                if (ispartialpage)
                {
                        /* Only asked to write a partial page */
                        LogwrtResult.Write = WriteRqst.Write;
                        break;
                }
                Write->curridx = NextBufIdx(Write->curridx);
        }

        /*
         * If asked to flush, do so
         */
        if (XLByteLT(LogwrtResult.Flush, WriteRqst.Flush) &&
                XLByteLT(LogwrtResult.Flush, LogwrtResult.Write))
        {
                /*
                 * Could get here without iterating above loop, in which case we
                 * might have no open file or the wrong one.  However, we do not
                 * need to fsync more than one file.
                 */
                if (sync_method != SYNC_METHOD_OPEN)
                {
                        if (openLogFile >= 0 &&
                         !XLByteInPrevSeg(LogwrtResult.Write, openLogId, openLogSeg))
                        {
                                if (close(openLogFile))
                                        ereport(PANIC,
                                                        (errcode_for_file_access(),
                                        errmsg("could not close log file %u, segment %u: %m",
                                                   openLogId, openLogSeg)));
                                openLogFile = -1;
                        }
                        if (openLogFile < 0)
                        {
                                XLByteToPrevSeg(LogwrtResult.Write, openLogId, openLogSeg);
                                openLogFile = XLogFileOpen(openLogId, openLogSeg);
                                openLogOff = 0;
                        }
                        issue_xlog_fsync();
                }
                LogwrtResult.Flush = LogwrtResult.Write;
        }

        /*
         * Update shared-memory status
         *
         * We make sure that the shared 'request' values do not fall behind the
         * 'result' values.  This is not absolutely essential, but it saves
         * some code in a couple of places.
         */
        {
                /* use volatile pointer to prevent code rearrangement */
                volatile XLogCtlData *xlogctl = XLogCtl;

                SpinLockAcquire_NoHoldoff(&xlogctl->info_lck);
                xlogctl->LogwrtResult = LogwrtResult;
                if (XLByteLT(xlogctl->LogwrtRqst.Write, LogwrtResult.Write))
                        xlogctl->LogwrtRqst.Write = LogwrtResult.Write;
                if (XLByteLT(xlogctl->LogwrtRqst.Flush, LogwrtResult.Flush))
                        xlogctl->LogwrtRqst.Flush = LogwrtResult.Flush;
                SpinLockRelease_NoHoldoff(&xlogctl->info_lck);
        }

        Write->LogwrtResult = LogwrtResult;
}

/*
 * Ensure that all XLOG data through the given position is flushed to disk.
 *
 * NOTE: this differs from XLogWrite mainly in that the WALWriteLock is not
 * already held, and we try to avoid acquiring it if possible.
 */
void
XLogFlush(XLogRecPtr record)
{
        XLogRecPtr      WriteRqstPtr;
        XLogwrtRqst WriteRqst;

        /* Disabled during REDO */
        if (InRedo)
                return;

        /* Quick exit if already known flushed */
        if (XLByteLE(record, LogwrtResult.Flush))
                return;

#ifdef WAL_DEBUG
        if (XLOG_DEBUG)
                elog(LOG, "xlog flush request %X/%X; write %X/%X; flush %X/%X",
                         record.xlogid, record.xrecoff,
                         LogwrtResult.Write.xlogid, LogwrtResult.Write.xrecoff,
                         LogwrtResult.Flush.xlogid, LogwrtResult.Flush.xrecoff);
#endif

        START_CRIT_SECTION();

        /*
         * Since fsync is usually a horribly expensive operation, we try to
         * piggyback as much data as we can on each fsync: if we see any more
         * data entered into the xlog buffer, we'll write and fsync that too,
         * so that the final value of LogwrtResult.Flush is as large as
         * possible. This gives us some chance of avoiding another fsync
         * immediately after.
         */

        /* initialize to given target; may increase below */
        WriteRqstPtr = record;

        /* read LogwrtResult and update local state */
        {
                /* use volatile pointer to prevent code rearrangement */
                volatile XLogCtlData *xlogctl = XLogCtl;

                SpinLockAcquire_NoHoldoff(&xlogctl->info_lck);
                if (XLByteLT(WriteRqstPtr, xlogctl->LogwrtRqst.Write))
                        WriteRqstPtr = xlogctl->LogwrtRqst.Write;
                LogwrtResult = xlogctl->LogwrtResult;
                SpinLockRelease_NoHoldoff(&xlogctl->info_lck);
        }

        /* done already? */
        if (!XLByteLE(record, LogwrtResult.Flush))
        {
                /* now wait for the write lock */
                LWLockAcquire(WALWriteLock, LW_EXCLUSIVE);
                LogwrtResult = XLogCtl->Write.LogwrtResult;
                if (!XLByteLE(record, LogwrtResult.Flush))
                {
                        /* try to write/flush later additions to XLOG as well */
                        if (LWLockConditionalAcquire(WALInsertLock, LW_EXCLUSIVE))
                        {
                                XLogCtlInsert *Insert = &XLogCtl->Insert;
                                uint32          freespace = INSERT_FREESPACE(Insert);

                                if (freespace < SizeOfXLogRecord)               /* buffer is full */
                                        WriteRqstPtr = XLogCtl->xlblocks[Insert->curridx];
                                else
                                {
                                        WriteRqstPtr = XLogCtl->xlblocks[Insert->curridx];
                                        WriteRqstPtr.xrecoff -= freespace;
                                }
                                LWLockRelease(WALInsertLock);
                                WriteRqst.Write = WriteRqstPtr;
                                WriteRqst.Flush = WriteRqstPtr;
                        }
                        else
                        {
                                WriteRqst.Write = WriteRqstPtr;
                                WriteRqst.Flush = record;
                        }
                        XLogWrite(WriteRqst);
                }
                LWLockRelease(WALWriteLock);
        }

        END_CRIT_SECTION();

        /*
         * If we still haven't flushed to the request point then we have a
         * problem; most likely, the requested flush point is past end of
         * XLOG. This has been seen to occur when a disk page has a corrupted
         * LSN.
         *
         * Formerly we treated this as a PANIC condition, but that hurts the
         * system's robustness rather than helping it: we do not want to take
         * down the whole system due to corruption on one data page.  In
         * particular, if the bad page is encountered again during recovery
         * then we would be unable to restart the database at all!      (This
         * scenario has actually happened in the field several times with 7.1
         * releases. Note that we cannot get here while InRedo is true, but if
         * the bad page is brought in and marked dirty during recovery then
         * CreateCheckPoint will try to flush it at the end of recovery.)
         *
         * The current approach is to ERROR under normal conditions, but only
         * WARNING during recovery, so that the system can be brought up even
         * if there's a corrupt LSN.  Note that for calls from xact.c, the
         * ERROR will be promoted to PANIC since xact.c calls this routine
         * inside a critical section.  However, calls from bufmgr.c are not
         * within critical sections and so we will not force a restart for a
         * bad LSN on a data page.
         */
        if (XLByteLT(LogwrtResult.Flush, record))
                elog(InRecovery ? WARNING : ERROR,
                         "xlog flush request %X/%X is not satisfied --- flushed only to %X/%X",
                         record.xlogid, record.xrecoff,
                         LogwrtResult.Flush.xlogid, LogwrtResult.Flush.xrecoff);
}

/*
 * Create a new XLOG file segment, or open a pre-existing one.
 *
 * log, seg: identify segment to be created/opened.
 *
 * *use_existent: if TRUE, OK to use a pre-existing file (else, any
 * pre-existing file will be deleted).  On return, TRUE if a pre-existing
 * file was used.
 *
 * use_lock: if TRUE, acquire ControlFileLock while moving file into
 * place.  This should be TRUE except during bootstrap log creation.  The
 * caller must *not* hold the lock at call.
 *
 * Returns FD of opened file.
 */
static int
XLogFileInit(uint32 log, uint32 seg,
                         bool *use_existent, bool use_lock)
{
        char            path[MAXPGPATH];
        char            tmppath[MAXPGPATH];
        char            zbuffer[BLCKSZ];
        int                     fd;
        int                     nbytes;

        XLogFilePath(path, ThisTimeLineID, log, seg);

        /*
         * Try to use existent file (checkpoint maker may have created it
         * already)
         */
        if (*use_existent)
        {
                fd = BasicOpenFile(path, O_RDWR | PG_BINARY | XLOG_SYNC_BIT,
                                                   S_IRUSR | S_IWUSR);
                if (fd < 0)
                {
                        if (errno != ENOENT)
                                ereport(PANIC,
                                                (errcode_for_file_access(),
                                                 errmsg("could not open file \"%s\" (log file %u, segment %u): %m",
                                                                path, log, seg)));
                }
                else
                        return (fd);
        }

        /*
         * Initialize an empty (all zeroes) segment.  NOTE: it is possible
         * that another process is doing the same thing.  If so, we will end
         * up pre-creating an extra log segment.  That seems OK, and better
         * than holding the lock throughout this lengthy process.
         */
        snprintf(tmppath, MAXPGPATH, "%s/xlogtemp.%d", XLogDir, getpid());

        unlink(tmppath);

        /* do not use XLOG_SYNC_BIT here --- want to fsync only at end of fill */
        fd = BasicOpenFile(tmppath, O_RDWR | O_CREAT | O_EXCL | PG_BINARY,
                                           S_IRUSR | S_IWUSR);
        if (fd < 0)
                ereport(PANIC,
                                (errcode_for_file_access(),
                                 errmsg("could not create file \"%s\": %m", tmppath)));

        /*
         * Zero-fill the file.  We have to do this the hard way to ensure that
         * all the file space has really been allocated --- on platforms that
         * allow "holes" in files, just seeking to the end doesn't allocate
         * intermediate space.  This way, we know that we have all the space
         * and (after the fsync below) that all the indirect blocks are down
         * on disk.  Therefore, fdatasync(2) or O_DSYNC will be sufficient to
         * sync future writes to the log file.
         */
        MemSet(zbuffer, 0, sizeof(zbuffer));
        for (nbytes = 0; nbytes < XLogSegSize; nbytes += sizeof(zbuffer))
        {
                errno = 0;
                if ((int) write(fd, zbuffer, sizeof(zbuffer)) != (int) sizeof(zbuffer))
                {
                        int                     save_errno = errno;

                        /*
                         * If we fail to make the file, delete it to release disk
                         * space
                         */
                        unlink(tmppath);
                        /* if write didn't set errno, assume problem is no disk space */
                        errno = save_errno ? save_errno : ENOSPC;

                        ereport(PANIC,
                                        (errcode_for_file_access(),
                                 errmsg("could not write to file \"%s\": %m", tmppath)));
                }
        }

        if (pg_fsync(fd) != 0)
                ereport(PANIC,
                                (errcode_for_file_access(),
                                 errmsg("could not fsync file \"%s\": %m", tmppath)));

        if (close(fd))
                ereport(PANIC,
                                (errcode_for_file_access(),
                                 errmsg("could not close file \"%s\": %m", tmppath)));

        /*
         * Now move the segment into place with its final name.
         *
         * If caller didn't want to use a pre-existing file, get rid of any
         * pre-existing file.  Otherwise, cope with possibility that someone
         * else has created the file while we were filling ours: if so, use
         * ours to pre-create a future log segment.
         */
        if (!InstallXLogFileSegment(log, seg, tmppath,
                                                                *use_existent, XLOGfileslop,
                                                                use_lock))
        {
                /* No need for any more future segments... */
                unlink(tmppath);
        }

        /* Set flag to tell caller there was no existent file */
        *use_existent = false;

        /* Now open original target segment (might not be file I just made) */
        fd = BasicOpenFile(path, O_RDWR | PG_BINARY | XLOG_SYNC_BIT,
                                           S_IRUSR | S_IWUSR);
        if (fd < 0)
                ereport(PANIC,
                                (errcode_for_file_access(),
                errmsg("could not open file \"%s\" (log file %u, segment %u): %m",
                           path, log, seg)));

        return (fd);
}

/*
 * Create a new XLOG file segment by copying a pre-existing one.
 *
 * log, seg: identify segment to be created.
 *
 * srcTLI, srclog, srcseg: identify segment to be copied (could be from
 *              a different timeline)
 *
 * Currently this is only used during recovery, and so there are no locking
 * considerations.      But we should be just as tense as XLogFileInit to avoid
 * emplacing a bogus file.
 */
static void
XLogFileCopy(uint32 log, uint32 seg,
                         TimeLineID srcTLI, uint32 srclog, uint32 srcseg)
{
        char            path[MAXPGPATH];
        char            tmppath[MAXPGPATH];
        char            buffer[BLCKSZ];
        int                     srcfd;
        int                     fd;
        int                     nbytes;

        /*
         * Open the source file
         */
        XLogFilePath(path, srcTLI, srclog, srcseg);
        srcfd = BasicOpenFile(path, O_RDONLY | PG_BINARY, 0);
        if (srcfd < 0)
                ereport(PANIC,
                                (errcode_for_file_access(),
                                 errmsg("could not open file \"%s\": %m", path)));

        /*
         * Copy into a temp file name.
         */
        snprintf(tmppath, MAXPGPATH, "%s/xlogtemp.%d", XLogDir, getpid());

        unlink(tmppath);

        /* do not use XLOG_SYNC_BIT here --- want to fsync only at end of fill */
        fd = BasicOpenFile(tmppath, O_RDWR | O_CREAT | O_EXCL | PG_BINARY,
                                           S_IRUSR | S_IWUSR);
        if (fd < 0)
                ereport(PANIC,
                                (errcode_for_file_access(),
                                 errmsg("could not create file \"%s\": %m", tmppath)));

        /*
         * Do the data copying.
         */
        for (nbytes = 0; nbytes < XLogSegSize; nbytes += sizeof(buffer))
        {
                errno = 0;
                if ((int) read(srcfd, buffer, sizeof(buffer)) != (int) sizeof(buffer))
                {
                        if (errno != 0)
                                ereport(PANIC,
                                                (errcode_for_file_access(),
                                                 errmsg("could not read file \"%s\": %m", path)));
                        else
                                ereport(PANIC,
                                         (errmsg("insufficient data in file \"%s\"", path)));
                }
                errno = 0;
                if ((int) write(fd, buffer, sizeof(buffer)) != (int) sizeof(buffer))
                {
                        int                     save_errno = errno;

                        /*
                         * If we fail to make the file, delete it to release disk
                         * space
                         */
                        unlink(tmppath);
                        /* if write didn't set errno, assume problem is no disk space */
                        errno = save_errno ? save_errno : ENOSPC;

                        ereport(PANIC,
                                        (errcode_for_file_access(),
                                 errmsg("could not write to file \"%s\": %m", tmppath)));
                }
        }

        if (pg_fsync(fd) != 0)
                ereport(PANIC,
                                (errcode_for_file_access(),
                                 errmsg("could not fsync file \"%s\": %m", tmppath)));

        if (close(fd))
                ereport(PANIC,
                                (errcode_for_file_access(),
                                 errmsg("could not close file \"%s\": %m", tmppath)));

        close(srcfd);

        /*
         * Now move the segment into place with its final name.
         */
        if (!InstallXLogFileSegment(log, seg, tmppath, false, 0, false))
                elog(PANIC, "InstallXLogFileSegment should not have failed");
}

/*
 * Install a new XLOG segment file as a current or future log segment.
 *
 * This is used both to install a newly-created segment (which has a temp
 * filename while it's being created) and to recycle an old segment.
 *
 * log, seg: identify segment to install as (or first possible target).
 *
 * tmppath: initial name of file to install.  It will be renamed into place.
 *
 * find_free: if TRUE, install the new segment at the first empty log/seg
 * number at or after the passed numbers.  If FALSE, install the new segment
 * exactly where specified, deleting any existing segment file there.
 *
 * max_advance: maximum number of log/seg slots to advance past the starting
 * point.  Fail if no free slot is found in this range.  (Irrelevant if
 * find_free is FALSE.)
 *
 * use_lock: if TRUE, acquire ControlFileLock while moving file into
 * place.  This should be TRUE except during bootstrap log creation.  The
 * caller must *not* hold the lock at call.
 *
 * Returns TRUE if file installed, FALSE if not installed because of
 * exceeding max_advance limit.  (Any other kind of failure causes ereport().)
 */
static bool
InstallXLogFileSegment(uint32 log, uint32 seg, char *tmppath,
                                           bool find_free, int max_advance,
                                           bool use_lock)
{
        char            path[MAXPGPATH];
        struct stat stat_buf;

        XLogFilePath(path, ThisTimeLineID, log, seg);

        /*
         * We want to be sure that only one process does this at a time.
         */
        if (use_lock)
                LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);

        if (!find_free)
        {
                /* Force installation: get rid of any pre-existing segment file */
                unlink(path);
        }
        else
        {
                /* Find a free slot to put it in */
                while (stat(path, &stat_buf) == 0)
                {
                        if (--max_advance < 0)
                        {
                                /* Failed to find a free slot within specified range */
                                if (use_lock)
                                        LWLockRelease(ControlFileLock);
                                return false;
                        }
                        NextLogSeg(log, seg);
                        XLogFilePath(path, ThisTimeLineID, log, seg);
                }
        }

        /*
         * Prefer link() to rename() here just to be really sure that we don't
         * overwrite an existing logfile.  However, there shouldn't be one, so
         * rename() is an acceptable substitute except for the truly paranoid.
         */
#if HAVE_WORKING_LINK
        if (link(tmppath, path) < 0)
                ereport(PANIC,
                                (errcode_for_file_access(),
                                 errmsg("could not link file \"%s\" to \"%s\" (initialization of log file %u, segment %u): %m",
                                                tmppath, path, log, seg)));
        unlink(tmppath);
#else
        if (rename(tmppath, path) < 0)
                ereport(PANIC,
                                (errcode_for_file_access(),
                                 errmsg("could not rename file \"%s\" to \"%s\" (initialization of log file %u, segment %u): %m",
                                                tmppath, path, log, seg)));
#endif

        if (use_lock)
                LWLockRelease(ControlFileLock);

        return true;
}

/*
 * Open a pre-existing logfile segment for writing.
 */
static int
XLogFileOpen(uint32 log, uint32 seg)
{
        char            path[MAXPGPATH];
        int                     fd;

        XLogFilePath(path, ThisTimeLineID, log, seg);

        fd = BasicOpenFile(path, O_RDWR | PG_BINARY | XLOG_SYNC_BIT,
                                           S_IRUSR | S_IWUSR);
        if (fd < 0)
                ereport(PANIC,
                                (errcode_for_file_access(),
                errmsg("could not open file \"%s\" (log file %u, segment %u): %m",
                           path, log, seg)));

        return fd;
}

/*
 * Open a logfile segment for reading (during recovery).
 */
static int
XLogFileRead(uint32 log, uint32 seg, int emode)
{
        char            path[MAXPGPATH];
        char            xlogfname[MAXFNAMELEN];
        ListCell   *cell;
        int                     fd;

        /*
         * Loop looking for a suitable timeline ID: we might need to read any
         * of the timelines listed in expectedTLIs.
         *
         * We expect curFileTLI on entry to be the TLI of the preceding file in
         * sequence, or 0 if there was no predecessor.  We do not allow
         * curFileTLI to go backwards; this prevents us from picking up the
         * wrong file when a parent timeline extends to higher segment numbers
         * than the child we want to read.
         */
        foreach(cell, expectedTLIs)
        {
                TimeLineID      tli = (TimeLineID) lfirst_int(cell);

                if (tli < curFileTLI)
                        break;                          /* don't bother looking at too-old TLIs */

                if (InArchiveRecovery)
                {
                        XLogFileName(xlogfname, tli, log, seg);
                        restoredFromArchive = RestoreArchivedFile(path, xlogfname,
                                                                                                          "RECOVERYXLOG",
                                                                                                          XLogSegSize);
                }
                else
                        XLogFilePath(path, tli, log, seg);

                fd = BasicOpenFile(path, O_RDONLY | PG_BINARY, 0);
                if (fd >= 0)
                {
                        /* Success! */
                        curFileTLI = tli;
                        return fd;
                }
                if (errno != ENOENT)    /* unexpected failure? */
                        ereport(PANIC,
                                        (errcode_for_file_access(),
                                         errmsg("could not open file \"%s\" (log file %u, segment %u): %m",
                                                        path, log, seg)));
        }

        /* Couldn't find it.  For simplicity, complain about front timeline */
        XLogFilePath(path, recoveryTargetTLI, log, seg);
        errno = ENOENT;
        ereport(emode,
                        (errcode_for_file_access(),
           errmsg("could not open file \"%s\" (log file %u, segment %u): %m",
                          path, log, seg)));
        return -1;
}

/*
 * Attempt to retrieve the specified file from off-line archival storage.
 * If successful, fill "path" with its complete path (note that this will be
 * a temp file name that doesn't follow the normal naming convention), and
 * return TRUE.
 *
 * If not successful, fill "path" with the name of the normal on-line file
 * (which may or may not actually exist, but we'll try to use it), and return
 * FALSE.
 *
 * For fixed-size files, the caller may pass the expected size as an
 * additional crosscheck on successful recovery.  If the file size is not
 * known, set expectedSize = 0.
 */
static bool
RestoreArchivedFile(char *path, const char *xlogfname,
                                        const char *recovername, off_t expectedSize)
{
        char            xlogpath[MAXPGPATH];
        char            xlogRestoreCmd[MAXPGPATH];
        char       *dp;
        char       *endp;
        const char *sp;
        int                     rc;
        struct stat stat_buf;

        /*
         * When doing archive recovery, we always prefer an archived log file
         * even if a file of the same name exists in XLogDir.  The reason is
         * that the file in XLogDir could be an old, un-filled or
         * partly-filled version that was copied and restored as part of
         * backing up $PGDATA.
         *
         * We could try to optimize this slightly by checking the local copy
         * lastchange timestamp against the archived copy, but we have no API
         * to do this, nor can we guarantee that the lastchange timestamp was
         * preserved correctly when we copied to archive. Our aim is
         * robustness, so we elect not to do this.
         *
         * If we cannot obtain the log file from the archive, however, we will
         * try to use the XLogDir file if it exists.  This is so that we can
         * make use of log segments that weren't yet transferred to the
         * archive.
         *
         * Notice that we don't actually overwrite any files when we copy back
         * from archive because the recoveryRestoreCommand may inadvertently
         * restore inappropriate xlogs, or they may be corrupt, so we may wish
         * to fallback to the segments remaining in current XLogDir later. The
         * copy-from-archive filename is always the same, ensuring that we
         * don't run out of disk space on long recoveries.
         */
        snprintf(xlogpath, MAXPGPATH, "%s/%s", XLogDir, recovername);

        /*
         * Make sure there is no existing file named recovername.
         */
        if (stat(xlogpath, &stat_buf) != 0)
        {
                if (errno != ENOENT)
                        ereport(FATAL,
                                        (errcode_for_file_access(),
                                         errmsg("could not stat \"%s\": %m",
                                                        xlogpath)));
        }
        else
        {
                if (unlink(xlogpath) != 0)
                        ereport(FATAL,
                                        (errcode_for_file_access(),
                                         errmsg("could not remove file \"%s\": %m",
                                                        xlogpath)));
        }

        /*
         * construct the command to be executed
         */
        dp = xlogRestoreCmd;
        endp = xlogRestoreCmd + MAXPGPATH - 1;
        *endp = '\0';

        for (sp = recoveryRestoreCommand; *sp; sp++)
        {
                if (*sp == '%')
                {
                        switch (sp[1])
                        {
                                case 'p':
                                        /* %p: full path of target file */
                                        sp++;
                                        StrNCpy(dp, xlogpath, endp - dp);
                                        make_native_path(dp);
                                        dp += strlen(dp);
                                        break;
                                case 'f':
                                        /* %f: filename of desired file */
                                        sp++;
                                        StrNCpy(dp, xlogfname, endp - dp);
                                        dp += strlen(dp);
                                        break;
                                case '%':
                                        /* convert %% to a single % */
                                        sp++;
                                        if (dp < endp)
                                                *dp++ = *sp;
                                        break;
                                default:
                                        /* otherwise treat the % as not special */
                                        if (dp < endp)
                                                *dp++ = *sp;
                                        break;
                        }
                }
                else
                {
                        if (dp < endp)
                                *dp++ = *sp;
                }
        }
        *dp = '\0';

        ereport(DEBUG3,
                        (errmsg_internal("executing restore command \"%s\"",
                                                         xlogRestoreCmd)));

        /*
         * Copy xlog from archival storage to XLogDir
         */
        rc = system(xlogRestoreCmd);
        if (rc == 0)
        {
                /*
                 * command apparently succeeded, but let's make sure the file is
                 * really there now and has the correct size.
                 *
                 * XXX I made wrong-size a fatal error to ensure the DBA would notice
                 * it, but is that too strong?  We could try to plow ahead with a
                 * local copy of the file ... but the problem is that there
                 * probably isn't one, and we'd incorrectly conclude we've reached
                 * the end of WAL and we're done recovering ...
                 */
                if (stat(xlogpath, &stat_buf) == 0)
                {
                        if (expectedSize > 0 && stat_buf.st_size != expectedSize)
                                ereport(FATAL,
                                                (errmsg("archive file \"%s\" has wrong size: %lu instead of %lu",
                                                                xlogfname,
                                                                (unsigned long) stat_buf.st_size,
                                                                (unsigned long) expectedSize)));
                        else
                        {
                                ereport(LOG,
                                                (errmsg("restored log file \"%s\" from archive",
                                                                xlogfname)));
                                strcpy(path, xlogpath);
                                return true;
                        }
                }
                else
                {
                        /* stat failed */
                        if (errno != ENOENT)
                                ereport(FATAL,
                                                (errcode_for_file_access(),
                                                 errmsg("could not stat \"%s\": %m",
                                                                xlogpath)));
                }
        }

        /*
         * remember, we rollforward UNTIL the restore fails so failure here is
         * just part of the process... that makes it difficult to determine
         * whether the restore failed because there isn't an archive to
         * restore, or because the administrator has specified the restore
         * program incorrectly.  We have to assume the former.
         */
        ereport(DEBUG1,
                 (errmsg("could not restore \"%s\" from archive: return code %d",
                                 xlogfname, rc)));

        /*
         * if an archived file is not available, there might still be a
         * version of this file in XLogDir, so return that as the filename to
         * open.
         *
         * In many recovery scenarios we expect this to fail also, but if so that
         * just means we've reached the end of WAL.
         */
        snprintf(path, MAXPGPATH, "%s/%s", XLogDir, xlogfname);
        return false;
}

/*
 * Preallocate log files beyond the specified log endpoint, according to
 * the XLOGfile user parameter.
 */
static void
PreallocXlogFiles(XLogRecPtr endptr)
{
        uint32          _logId;
        uint32          _logSeg;
        int                     lf;
        bool            use_existent;

        XLByteToPrevSeg(endptr, _logId, _logSeg);
        if ((endptr.xrecoff - 1) % XLogSegSize >=
                (uint32) (0.75 * XLogSegSize))
        {
                NextLogSeg(_logId, _logSeg);
                use_existent = true;
                lf = XLogFileInit(_logId, _logSeg, &use_existent, true);
                close(lf);
        }
}

/*
 * Remove or move offline all log files older or equal to passed log/seg#
 *
 * endptr is current (or recent) end of xlog; this is used to determine
 * whether we want to recycle rather than delete no-longer-wanted log files.
 */
static void
MoveOfflineLogs(uint32 log, uint32 seg, XLogRecPtr endptr)
{
        uint32          endlogId;
        uint32          endlogSeg;
        DIR                *xldir;
        struct dirent *xlde;
        char            lastoff[MAXFNAMELEN];
        char            path[MAXPGPATH];

        XLByteToPrevSeg(endptr, endlogId, endlogSeg);

        xldir = AllocateDir(XLogDir);
        if (xldir == NULL)
                ereport(ERROR,
                                (errcode_for_file_access(),
                        errmsg("could not open transaction log directory \"%s\": %m",
                                   XLogDir)));

        XLogFileName(lastoff, ThisTimeLineID, log, seg);

        errno = 0;
        while ((xlde = readdir(xldir)) != NULL)
        {
                /*
                 * We ignore the timeline part of the XLOG segment identifiers in
                 * deciding whether a segment is still needed.  This ensures that
                 * we won't prematurely remove a segment from a parent timeline.
                 * We could probably be a little more proactive about removing
                 * segments of non-parent timelines, but that would be a whole lot
                 * more complicated.
                 *
                 * We use the alphanumeric sorting property of the filenames to
                 * decide which ones are earlier than the lastoff segment.
                 */
                if (strlen(xlde->d_name) == 24 &&
                        strspn(xlde->d_name, "0123456789ABCDEF") == 24 &&
                        strcmp(xlde->d_name + 8, lastoff + 8) <= 0)
                {
                        bool            recycle;

                        if (XLogArchivingActive())
                                recycle = XLogArchiveIsDone(xlde->d_name);
                        else
                                recycle = true;

                        if (recycle)
                        {
                                snprintf(path, MAXPGPATH, "%s/%s", XLogDir, xlde->d_name);

                                /*
                                 * Before deleting the file, see if it can be recycled as
                                 * a future log segment.  We allow recycling segments up
                                 * to XLOGfileslop segments beyond the current XLOG
                                 * location.
                                 */
                                if (InstallXLogFileSegment(endlogId, endlogSeg, path,
                                                                                   true, XLOGfileslop,
                                                                                   true))
                                {
                                        ereport(DEBUG1,
                                                  (errmsg("recycled transaction log file \"%s\"",
                                                                  xlde->d_name)));
                                }
                                else
                                {
                                        /* No need for any more future segments... */
                                        ereport(DEBUG1,
                                                  (errmsg("removing transaction log file \"%s\"",
                                                                  xlde->d_name)));
                                        unlink(path);
                                }

                                XLogArchiveCleanup(xlde->d_name);
                        }
                }
                errno = 0;
        }
#ifdef WIN32

        /*
         * This fix is in mingw cvs (runtime/mingwex/dirent.c rev 1.4), but
         * not in released version
         */
        if (GetLastError() == ERROR_NO_MORE_FILES)
                errno = 0;
#endif
        if (errno)
                ereport(ERROR,
                                (errcode_for_file_access(),
                        errmsg("could not read transaction log directory \"%s\": %m",
                                   XLogDir)));
        FreeDir(xldir);
}

/*
 * Restore the backup blocks present in an XLOG record, if any.
 *
 * We assume all of the record has been read into memory at *record.
 *
 * Note: when a backup block is available in XLOG, we restore it
 * unconditionally, even if the page in the database appears newer.
 * This is to protect ourselves against database pages that were partially
 * or incorrectly written during a crash.  We assume that the XLOG data
 * must be good because it has passed a CRC check, while the database
 * page might not be.  This will force us to replay all subsequent
 * modifications of the page that appear in XLOG, rather than possibly
 * ignoring them as already applied, but that's not a huge drawback.
 */
static void
RestoreBkpBlocks(XLogRecord *record, XLogRecPtr lsn)
{
        Relation        reln;
        Buffer          buffer;
        Page            page;
        BkpBlock        bkpb;
        char       *blk;
        int                     i;

        blk = (char *) XLogRecGetData(record) + record->xl_len;
        for (i = 0; i < XLR_MAX_BKP_BLOCKS; i++)
        {
                if (!(record->xl_info & XLR_SET_BKP_BLOCK(i)))
                        continue;

                memcpy((char *) &bkpb, blk, sizeof(BkpBlock));
                blk += sizeof(BkpBlock);

                reln = XLogOpenRelation(true, record->xl_rmid, bkpb.node);

                if (reln)
                {
                        buffer = XLogReadBuffer(true, reln, bkpb.block);
                        if (BufferIsValid(buffer))
                        {
                                page = (Page) BufferGetPage(buffer);
                                memcpy((char *) page, blk, BLCKSZ);
                                PageSetLSN(page, lsn);
                                PageSetTLI(page, ThisTimeLineID);
                                LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
                                WriteBuffer(buffer);
                        }
                }

                blk += BLCKSZ;
        }
}

/*
 * CRC-check an XLOG record.  We do not believe the contents of an XLOG
 * record (other than to the minimal extent of computing the amount of
 * data to read in) until we've checked the CRCs.
 *
 * We assume all of the record has been read into memory at *record.
 */
static bool
RecordIsValid(XLogRecord *record, XLogRecPtr recptr, int emode)
{
        crc64           crc;
        crc64           cbuf;
        int                     i;
        uint32          len = record->xl_len;
        char       *blk;

        /* Check CRC of rmgr data and record header */
        INIT_CRC64(crc);
        COMP_CRC64(crc, XLogRecGetData(record), len);
        COMP_CRC64(crc, (char *) record + sizeof(crc64),
                           SizeOfXLogRecord - sizeof(crc64));
        FIN_CRC64(crc);

        if (!EQ_CRC64(record->xl_crc, crc))
        {
                ereport(emode,
                                (errmsg("incorrect resource manager data checksum in record at %X/%X",
                                                recptr.xlogid, recptr.xrecoff)));
                return (false);
        }

        /* Check CRCs of backup blocks, if any */
        blk = (char *) XLogRecGetData(record) + len;
        for (i = 0; i < XLR_MAX_BKP_BLOCKS; i++)
        {
                if (!(record->xl_info & XLR_SET_BKP_BLOCK(i)))
                        continue;

                INIT_CRC64(crc);
                COMP_CRC64(crc, blk + sizeof(BkpBlock), BLCKSZ);
                COMP_CRC64(crc, blk + sizeof(crc64),
                                   sizeof(BkpBlock) - sizeof(crc64));
                FIN_CRC64(crc);
                memcpy((char *) &cbuf, blk, sizeof(crc64));             /* don't assume
                                                                                                                 * alignment */

                if (!EQ_CRC64(cbuf, crc))
                {
                        ereport(emode,
                                        (errmsg("incorrect checksum of backup block %d in record at %X/%X",
                                                        i + 1, recptr.xlogid, recptr.xrecoff)));
                        return (false);
                }
                blk += sizeof(BkpBlock) + BLCKSZ;
        }

        return (true);
}

/*
 * Attempt to read an XLOG record.
 *
 * If RecPtr is not NULL, try to read a record at that position.  Otherwise
 * try to read a record just after the last one previously read.
 *
 * If no valid record is available, returns NULL, or fails if emode is PANIC.
 * (emode must be either PANIC or LOG.)
 *
 * The record is copied into readRecordBuf, so that on successful return,
 * the returned record pointer always points there.
 */
static XLogRecord *
ReadRecord(XLogRecPtr *RecPtr, int emode)
{
        XLogRecord *record;
        char       *buffer;
        XLogRecPtr      tmpRecPtr = EndRecPtr;
        bool            randAccess = false;
        uint32          len,
                                total_len;
        uint32          targetPageOff;
        uint32          targetRecOff;
        uint32          pageHeaderSize;
        unsigned        i;

        if (readBuf == NULL)
        {
                /*
                 * First time through, permanently allocate readBuf.  We do it
                 * this way, rather than just making a static array, for two
                 * reasons: (1) no need to waste the storage in most
                 * instantiations of the backend; (2) a static char array isn't
                 * guaranteed to have any particular alignment, whereas malloc()
                 * will provide MAXALIGN'd storage.
                 */
                readBuf = (char *) malloc(BLCKSZ);
                Assert(readBuf != NULL);
        }

        if (RecPtr == NULL)
        {
                RecPtr = &tmpRecPtr;
                /* fast case if next record is on same page */
                if (nextRecord != NULL)
                {
                        record = nextRecord;
                        goto got_record;
                }
                /* align old recptr to next page */
                if (tmpRecPtr.xrecoff % BLCKSZ != 0)
                        tmpRecPtr.xrecoff += (BLCKSZ - tmpRecPtr.xrecoff % BLCKSZ);
                if (tmpRecPtr.xrecoff >= XLogFileSize)
                {
                        (tmpRecPtr.xlogid)++;
                        tmpRecPtr.xrecoff = 0;
                }
                /* We will account for page header size below */
        }
        else
        {
                if (!XRecOffIsValid(RecPtr->xrecoff))
                        ereport(PANIC,
                                        (errmsg("invalid record offset at %X/%X",
                                                        RecPtr->xlogid, RecPtr->xrecoff)));

                /*
                 * Since we are going to a random position in WAL, forget any
                 * prior state about what timeline we were in, and allow it to be
                 * any timeline in expectedTLIs.  We also set a flag to allow
                 * curFileTLI to go backwards (but we can't reset that variable
                 * right here, since we might not change files at all).
                 */
                lastPageTLI = 0;                /* see comment in ValidXLOGHeader */
                randAccess = true;              /* allow curFileTLI to go backwards too */
        }

        if (readFile >= 0 && !XLByteInSeg(*RecPtr, readId, readSeg))
        {
                close(readFile);
                readFile = -1;
        }
        XLByteToSeg(*RecPtr, readId, readSeg);
        if (readFile < 0)
        {
                /* Now it's okay to reset curFileTLI if random fetch */
                if (randAccess)
                        curFileTLI = 0;

                readFile = XLogFileRead(readId, readSeg, emode);
                if (readFile < 0)
                        goto next_record_is_invalid;
                readOff = (uint32) (-1);        /* force read to occur below */
        }

        targetPageOff = ((RecPtr->xrecoff % XLogSegSize) / BLCKSZ) * BLCKSZ;
        if (readOff != targetPageOff)
        {
                readOff = targetPageOff;
                if (lseek(readFile, (off_t) readOff, SEEK_SET) < 0)
                {
                        ereport(emode,
                                        (errcode_for_file_access(),
                                         errmsg("could not seek in log file %u, segment %u to offset %u: %m",
                                                        readId, readSeg, readOff)));
                        goto next_record_is_invalid;
                }
                if (read(readFile, readBuf, BLCKSZ) != BLCKSZ)
                {
                        ereport(emode,
                                        (errcode_for_file_access(),
                                         errmsg("could not read from log file %u, segment %u at offset %u: %m",
                                                        readId, readSeg, readOff)));
                        goto next_record_is_invalid;
                }
                if (!ValidXLOGHeader((XLogPageHeader) readBuf, emode))
                        goto next_record_is_invalid;
        }
        pageHeaderSize = XLogPageHeaderSize((XLogPageHeader) readBuf);
        targetRecOff = RecPtr->xrecoff % BLCKSZ;
        if (targetRecOff == 0)
        {
                /*
                 * Can only get here in the continuing-from-prev-page case,
                 * because XRecOffIsValid eliminated the zero-page-offset case
                 * otherwise. Need to skip over the new page's header.
                 */
                tmpRecPtr.xrecoff += pageHeaderSize;
                targetRecOff = pageHeaderSize;
        }
        else if (targetRecOff < pageHeaderSize)
        {
                ereport(emode,
                                (errmsg("invalid record offset at %X/%X",
                                                RecPtr->xlogid, RecPtr->xrecoff)));
                goto next_record_is_invalid;
        }
        if ((((XLogPageHeader) readBuf)->xlp_info & XLP_FIRST_IS_CONTRECORD) &&
                targetRecOff == pageHeaderSize)
        {
                ereport(emode,
                                (errmsg("contrecord is requested by %X/%X",
                                                RecPtr->xlogid, RecPtr->xrecoff)));
                goto next_record_is_invalid;
        }
        record = (XLogRecord *) ((char *) readBuf + RecPtr->xrecoff % BLCKSZ);

got_record:;

        /*
         * Currently, xl_len == 0 must be bad data, but that might not be true
         * forever.  See note in XLogInsert.
         */
        if (record->xl_len == 0)
        {
                ereport(emode,
                                (errmsg("record with zero length at %X/%X",
                                                RecPtr->xlogid, RecPtr->xrecoff)));
                goto next_record_is_invalid;
        }
        if (record->xl_rmid > RM_MAX_ID)
        {
                ereport(emode,
                                (errmsg("invalid resource manager ID %u at %X/%X",
                                         record->xl_rmid, RecPtr->xlogid, RecPtr->xrecoff)));
                goto next_record_is_invalid;
        }

        /*
         * Compute total length of record including any appended backup
         * blocks.
         */
        total_len = SizeOfXLogRecord + record->xl_len;
        for (i = 0; i < XLR_MAX_BKP_BLOCKS; i++)
        {
                if (!(record->xl_info & XLR_SET_BKP_BLOCK(i)))
                        continue;
                total_len += sizeof(BkpBlock) + BLCKSZ;
        }

        /*
         * Allocate or enlarge readRecordBuf as needed.  To avoid useless
         * small increases, round its size to a multiple of BLCKSZ, and make
         * sure it's at least 4*BLCKSZ to start with.  (That is enough for all
         * "normal" records, but very large commit or abort records might need
         * more space.)
         */
        if (total_len > readRecordBufSize)
        {
                uint32          newSize = total_len;

                newSize += BLCKSZ - (newSize % BLCKSZ);
                newSize = Max(newSize, 4 * BLCKSZ);
                if (readRecordBuf)
                        free(readRecordBuf);
                readRecordBuf = (char *) malloc(newSize);
                if (!readRecordBuf)
                {
                        readRecordBufSize = 0;
                        /* We treat this as a "bogus data" condition */
                        ereport(emode,
                                        (errmsg("record length %u at %X/%X too long",
                                                        total_len, RecPtr->xlogid, RecPtr->xrecoff)));
                        goto next_record_is_invalid;
                }
                readRecordBufSize = newSize;
        }

        buffer = readRecordBuf;
        nextRecord = NULL;
        len = BLCKSZ - RecPtr->xrecoff % BLCKSZ;
        if (total_len > len)
        {
                /* Need to reassemble record */
                XLogContRecord *contrecord;
                uint32          gotlen = len;

                memcpy(buffer, record, len);
                record = (XLogRecord *) buffer;
                buffer += len;
                for (;;)
                {
                        readOff += BLCKSZ;
                        if (readOff >= XLogSegSize)
                        {
                                close(readFile);
                                readFile = -1;
                                NextLogSeg(readId, readSeg);
                                readFile = XLogFileRead(readId, readSeg, emode);
                                if (readFile < 0)
                                        goto next_record_is_invalid;
                                readOff = 0;
                        }
                        if (read(readFile, readBuf, BLCKSZ) != BLCKSZ)
                        {
                                ereport(emode,
                                                (errcode_for_file_access(),
                                                 errmsg("could not read from log file %u, segment %u, offset %u: %m",
                                                                readId, readSeg, readOff)));
                                goto next_record_is_invalid;
                        }
                        if (!ValidXLOGHeader((XLogPageHeader) readBuf, emode))
                                goto next_record_is_invalid;
                        if (!(((XLogPageHeader) readBuf)->xlp_info & XLP_FIRST_IS_CONTRECORD))
                        {
                                ereport(emode,
                                                (errmsg("there is no contrecord flag in log file %u, segment %u, offset %u",
                                                                readId, readSeg, readOff)));
                                goto next_record_is_invalid;
                        }
                        pageHeaderSize = XLogPageHeaderSize((XLogPageHeader) readBuf);
                        contrecord = (XLogContRecord *) ((char *) readBuf + pageHeaderSize);
                        if (contrecord->xl_rem_len == 0 ||
                                total_len != (contrecord->xl_rem_len + gotlen))
                        {
                                ereport(emode,
                                                (errmsg("invalid contrecord length %u in log file %u, segment %u, offset %u",
                                                                contrecord->xl_rem_len,
                                                                readId, readSeg, readOff)));
                                goto next_record_is_invalid;
                        }
                        len = BLCKSZ - pageHeaderSize - SizeOfXLogContRecord;
                        if (contrecord->xl_rem_len > len)
                        {
                                memcpy(buffer, (char *) contrecord + SizeOfXLogContRecord, len);
                                gotlen += len;
                                buffer += len;
                                continue;
                        }
                        memcpy(buffer, (char *) contrecord + SizeOfXLogContRecord,
                                   contrecord->xl_rem_len);
                        break;
                }
                if (!RecordIsValid(record, *RecPtr, emode))
                        goto next_record_is_invalid;
                pageHeaderSize = XLogPageHeaderSize((XLogPageHeader) readBuf);
                if (BLCKSZ - SizeOfXLogRecord >= pageHeaderSize +
                        SizeOfXLogContRecord + MAXALIGN(contrecord->xl_rem_len))
                {
                        nextRecord = (XLogRecord *) ((char *) contrecord +
                                SizeOfXLogContRecord + MAXALIGN(contrecord->xl_rem_len));
                }
                EndRecPtr.xlogid = readId;
                EndRecPtr.xrecoff = readSeg * XLogSegSize + readOff +
                        pageHeaderSize + SizeOfXLogContRecord +
                        MAXALIGN(contrecord->xl_rem_len);
                ReadRecPtr = *RecPtr;
                return record;
        }

        /* Record does not cross a page boundary */
        if (!RecordIsValid(record, *RecPtr, emode))
                goto next_record_is_invalid;
        if (BLCKSZ - SizeOfXLogRecord >= RecPtr->xrecoff % BLCKSZ +
                MAXALIGN(total_len))
                nextRecord = (XLogRecord *) ((char *) record + MAXALIGN(total_len));
        EndRecPtr.xlogid = RecPtr->xlogid;
        EndRecPtr.xrecoff = RecPtr->xrecoff + MAXALIGN(total_len);
        ReadRecPtr = *RecPtr;
        memcpy(buffer, record, total_len);
        return (XLogRecord *) buffer;

next_record_is_invalid:;
        close(readFile);
        readFile = -1;
        nextRecord = NULL;
        return NULL;
}

/*
 * Check whether the xlog header of a page just read in looks valid.
 *
 * This is just a convenience subroutine to avoid duplicated code in
 * ReadRecord.  It's not intended for use from anywhere else.
 */
static bool
ValidXLOGHeader(XLogPageHeader hdr, int emode)
{
        XLogRecPtr      recaddr;

        if (hdr->xlp_magic != XLOG_PAGE_MAGIC)
        {
                ereport(emode,
                                (errmsg("invalid magic number %04X in log file %u, segment %u, offset %u",
                                                hdr->xlp_magic, readId, readSeg, readOff)));
                return false;
        }
        if ((hdr->xlp_info & ~XLP_ALL_FLAGS) != 0)
        {
                ereport(emode,
                                (errmsg("invalid info bits %04X in log file %u, segment %u, offset %u",
                                                hdr->xlp_info, readId, readSeg, readOff)));
                return false;
        }
        if (hdr->xlp_info & XLP_LONG_HEADER)
        {
                XLogLongPageHeader longhdr = (XLogLongPageHeader) hdr;

                if (longhdr->xlp_sysid != ControlFile->system_identifier)
                {
                        char            fhdrident_str[32];
                        char            sysident_str[32];

                        /*
                         * Format sysids separately to keep platform-dependent format
                         * code out of the translatable message string.
                         */
                        snprintf(fhdrident_str, sizeof(fhdrident_str), UINT64_FORMAT,
                                         longhdr->xlp_sysid);
                        snprintf(sysident_str, sizeof(sysident_str), UINT64_FORMAT,
                                         ControlFile->system_identifier);
                        ereport(emode,
                                        (errmsg("WAL file is from different system"),
                                errdetail("WAL file SYSID is %s, pg_control SYSID is %s",
                                                  fhdrident_str, sysident_str)));
                        return false;
                }
                if (longhdr->xlp_seg_size != XLogSegSize)
                {
                        ereport(emode,
                                        (errmsg("WAL file is from different system"),
                                  errdetail("Incorrect XLOG_SEG_SIZE in page header.")));
                        return false;
                }
        }
        recaddr.xlogid = readId;
        recaddr.xrecoff = readSeg * XLogSegSize + readOff;
        if (!XLByteEQ(hdr->xlp_pageaddr, recaddr))
        {
                ereport(emode,
                                (errmsg("unexpected pageaddr %X/%X in log file %u, segment %u, offset %u",
                                         hdr->xlp_pageaddr.xlogid, hdr->xlp_pageaddr.xrecoff,
                                                readId, readSeg, readOff)));
                return false;
        }

        /*
         * Check page TLI is one of the expected values.
         */
        if (!list_member_int(expectedTLIs, (int) hdr->xlp_tli))
        {
                ereport(emode,
                                (errmsg("unexpected timeline ID %u in log file %u, segment %u, offset %u",
                                                hdr->xlp_tli,
                                                readId, readSeg, readOff)));
                return false;
        }

        /*
         * Since child timelines are always assigned a TLI greater than their
         * immediate parent's TLI, we should never see TLI go backwards across
         * successive pages of a consistent WAL sequence.
         *
         * Of course this check should only be applied when advancing
         * sequentially across pages; therefore ReadRecord resets lastPageTLI
         * to zero when going to a random page.
         */
        if (hdr->xlp_tli < lastPageTLI)
        {
                ereport(emode,
                                (errmsg("out-of-sequence timeline ID %u (after %u) in log file %u, segment %u, offset %u",
                                                hdr->xlp_tli, lastPageTLI,
                                                readId, readSeg, readOff)));
                return false;
        }
        lastPageTLI = hdr->xlp_tli;
        return true;
}

/*
 * Try to read a timeline's history file.
 *
 * If successful, return the list of component TLIs (the given TLI followed by
 * its ancestor TLIs).  If we can't find the history file, assume that the
 * timeline has no parents, and return a list of just the specified timeline
 * ID.
 */
static List *
readTimeLineHistory(TimeLineID targetTLI)
{
        List       *result;
        char            path[MAXPGPATH];
        char            histfname[MAXFNAMELEN];
        char            fline[MAXPGPATH];
        FILE       *fd;

        if (InArchiveRecovery)
        {
                TLHistoryFileName(histfname, targetTLI);
                RestoreArchivedFile(path, histfname, "RECOVERYHISTORY", 0);
        }
        else
                TLHistoryFilePath(path, targetTLI);

        fd = AllocateFile(path, "r");
        if (fd == NULL)
        {
                if (errno != ENOENT)
                        ereport(FATAL,
                                        (errcode_for_file_access(),
                                         errmsg("could not open \"%s\": %m", path)));
                /* Not there, so assume no parents */
                return list_make1_int((int) targetTLI);
        }

        result = NIL;

        /*
         * Parse the file...
         */
        while (fgets(fline, MAXPGPATH, fd) != NULL)
        {
                /* skip leading whitespace and check for # comment */
                char       *ptr;
                char       *endptr;
                TimeLineID      tli;

                for (ptr = fline; *ptr; ptr++)
                {
                        if (!isspace((unsigned char) *ptr))
                                break;
                }
                if (*ptr == '\0' || *ptr == '#')
                        continue;

                /* expect a numeric timeline ID as first field of line */
                tli = (TimeLineID) strtoul(ptr, &endptr, 0);
                if (endptr == ptr)
                        ereport(FATAL,
                                        (errmsg("syntax error in history file: %s", fline),
                                         errhint("Expected a numeric timeline ID.")));

                if (result &&
                        tli <= (TimeLineID) linitial_int(result))
                        ereport(FATAL,
                                        (errmsg("invalid data in history file: %s", fline),
                           errhint("Timeline IDs must be in increasing sequence.")));

                /* Build list with newest item first */
                result = lcons_int((int) tli, result);

                /* we ignore the remainder of each line */
        }

        FreeFile(fd);

        if (result &&
                targetTLI <= (TimeLineID) linitial_int(result))
                ereport(FATAL,
                                (errmsg("invalid data in history file \"%s\"", path),
                errhint("Timeline IDs must be less than child timeline's ID.")));

        result = lcons_int((int) targetTLI, result);

        ereport(DEBUG3,
                        (errmsg_internal("history of timeline %u is %s",
                                                         targetTLI, nodeToString(result))));

        return result;
}

/*
 * Probe whether a timeline history file exists for the given timeline ID
 */
static bool
existsTimeLineHistory(TimeLineID probeTLI)
{
        char            path[MAXPGPATH];
        char            histfname[MAXFNAMELEN];
        FILE       *fd;

        if (InArchiveRecovery)
        {
                TLHistoryFileName(histfname, probeTLI);
                RestoreArchivedFile(path, histfname, "RECOVERYHISTORY", 0);
        }
        else
                TLHistoryFilePath(path, probeTLI);

        fd = AllocateFile(path, "r");
        if (fd != NULL)
        {
                FreeFile(fd);
                return true;
        }
        else
        {
                if (errno != ENOENT)
                        ereport(FATAL,
                                        (errcode_for_file_access(),
                                         errmsg("could not open \"%s\": %m", path)));
                return false;
        }
}

/*
 * Find the newest existing timeline, assuming that startTLI exists.
 *
 * Note: while this is somewhat heuristic, it does positively guarantee
 * that (result + 1) is not a known timeline, and therefore it should
 * be safe to assign that ID to a new timeline.
 */
static TimeLineID
findNewestTimeLine(TimeLineID startTLI)
{
        TimeLineID      newestTLI;
        TimeLineID      probeTLI;

        /*
         * The algorithm is just to probe for the existence of timeline
         * history files.  XXX is it useful to allow gaps in the sequence?
         */
        newestTLI = startTLI;

        for (probeTLI = startTLI + 1;; probeTLI++)
        {
                if (existsTimeLineHistory(probeTLI))
                {
                        newestTLI = probeTLI;           /* probeTLI exists */
                }
                else
                {
                        /* doesn't exist, assume we're done */
                        break;
                }
        }

        return newestTLI;
}

/*
 * Create a new timeline history file.
 *
 *      newTLI: ID of the new timeline
 *      parentTLI: ID of its immediate parent
 *      endTLI et al: ID of the last used WAL file, for annotation purposes
 *
 * Currently this is only used during recovery, and so there are no locking
 * considerations.      But we should be just as tense as XLogFileInit to avoid
 * emplacing a bogus file.
 */
static void
writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI,
                                         TimeLineID endTLI, uint32 endLogId, uint32 endLogSeg)
{
        char            path[MAXPGPATH];
        char            tmppath[MAXPGPATH];
        char            histfname[MAXFNAMELEN];
        char            xlogfname[MAXFNAMELEN];
        char            buffer[BLCKSZ];
        int                     srcfd;
        int                     fd;
        int                     nbytes;

        Assert(newTLI > parentTLI); /* else bad selection of newTLI */

        /*
         * Write into a temp file name.
         */
        snprintf(tmppath, MAXPGPATH, "%s/xlogtemp.%d", XLogDir, getpid());

        unlink(tmppath);

        /* do not use XLOG_SYNC_BIT here --- want to fsync only at end of fill */
        fd = BasicOpenFile(tmppath, O_RDWR | O_CREAT | O_EXCL,
                                           S_IRUSR | S_IWUSR);
        if (fd < 0)
                ereport(PANIC,
                                (errcode_for_file_access(),
                                 errmsg("could not create file \"%s\": %m", tmppath)));

        /*
         * If a history file exists for the parent, copy it verbatim
         */
        if (InArchiveRecovery)
        {
                TLHistoryFileName(histfname, parentTLI);
                RestoreArchivedFile(path, histfname, "RECOVERYHISTORY", 0);
        }
        else
                TLHistoryFilePath(path, parentTLI);

        srcfd = BasicOpenFile(path, O_RDONLY, 0);
        if (srcfd < 0)
        {
                if (errno != ENOENT)
                        ereport(FATAL,
                                        (errcode_for_file_access(),
                                         errmsg("could not open \"%s\": %m", path)));
                /* Not there, so assume parent has no parents */
        }
        else
        {
                for (;;)
                {
                        errno = 0;
                        nbytes = (int) read(srcfd, buffer, sizeof(buffer));
                        if (nbytes < 0 || errno != 0)
                                ereport(PANIC,
                                                (errcode_for_file_access(),
                                                 errmsg("could not read file \"%s\": %m", path)));
                        if (nbytes == 0)
                                break;
                        errno = 0;
                        if ((int) write(fd, buffer, nbytes) != nbytes)
                        {
                                int                     save_errno = errno;

                                /*
                                 * If we fail to make the file, delete it to release disk
                                 * space
                                 */
                                unlink(tmppath);

                                /*
                                 * if write didn't set errno, assume problem is no disk
                                 * space
                                 */
                                errno = save_errno ? save_errno : ENOSPC;

                                ereport(PANIC,
                                                (errcode_for_file_access(),
                                 errmsg("could not write to file \"%s\": %m", tmppath)));
                        }
                }
                close(srcfd);
        }

        /*
         * Append one line with the details of this timeline split.
         *
         * If we did have a parent file, insert an extra newline just in case the
         * parent file failed to end with one.
         */
        XLogFileName(xlogfname, endTLI, endLogId, endLogSeg);

        snprintf(buffer, sizeof(buffer),
                         "%s%u\t%s\t%s transaction %u at %s\n",
                         (srcfd < 0) ? "" : "\n",
                         parentTLI,
                         xlogfname,
                         recoveryStopAfter ? "after" : "before",
                         recoveryStopXid,
                         str_time(recoveryStopTime));

        nbytes = strlen(buffer);
        errno = 0;
        if ((int) write(fd, buffer, nbytes) != nbytes)
        {
                int                     save_errno = errno;

                /*
                 * If we fail to make the file, delete it to release disk space
                 */
                unlink(tmppath);
                /* if write didn't set errno, assume problem is no disk space */
                errno = save_errno ? save_errno : ENOSPC;

                ereport(PANIC,
                                (errcode_for_file_access(),
                                 errmsg("could not write to file \"%s\": %m", tmppath)));
        }

        if (pg_fsync(fd) != 0)
                ereport(PANIC,
                                (errcode_for_file_access(),
                                 errmsg("could not fsync file \"%s\": %m", tmppath)));

        if (close(fd))
                ereport(PANIC,
                                (errcode_for_file_access(),
                                 errmsg("could not close file \"%s\": %m", tmppath)));


        /*
         * Now move the completed history file into place with its final name.
         */
        TLHistoryFilePath(path, newTLI);

        /*
         * Prefer link() to rename() here just to be really sure that we don't
         * overwrite an existing logfile.  However, there shouldn't be one, so
         * rename() is an acceptable substitute except for the truly paranoid.
         */
#if HAVE_WORKING_LINK
        if (link(tmppath, path) < 0)
                ereport(PANIC,
                                (errcode_for_file_access(),
                                 errmsg("could not link file \"%s\" to \"%s\": %m",
                                                tmppath, path)));
        unlink(tmppath);
#else
        if (rename(tmppath, path) < 0)
                ereport(PANIC,
                                (errcode_for_file_access(),
                                 errmsg("could not rename file \"%s\" to \"%s\": %m",
                                                tmppath, path)));
#endif

        /* The history file can be archived immediately. */
        TLHistoryFileName(histfname, newTLI);
        XLogArchiveNotify(histfname);
}

/*
 * I/O routines for pg_control
 *
 * *ControlFile is a buffer in shared memory that holds an image of the
 * contents of pg_control.      WriteControlFile() initializes pg_control
 * given a preloaded buffer, ReadControlFile() loads the buffer from
 * the pg_control file (during postmaster or standalone-backend startup),
 * and UpdateControlFile() rewrites pg_control after we modify xlog state.
 *
 * For simplicity, WriteControlFile() initializes the fields of pg_control
 * that are related to checking backend/database compatibility, and
 * ReadControlFile() verifies they are correct.  We could split out the
 * I/O and compatibility-check functions, but there seems no need currently.
 */

void
XLOGPathInit(void)
{
        /* Init XLOG file paths */
        snprintf(XLogDir, MAXPGPATH, "%s/pg_xlog", DataDir);
        snprintf(ControlFilePath, MAXPGPATH, "%s/global/pg_control", DataDir);
}

static void
WriteControlFile(void)
{
        int                     fd;
        char            buffer[BLCKSZ]; /* need not be aligned */
        char       *localeptr;

        /*
         * Initialize version and compatibility-check fields
         */
        ControlFile->pg_control_version = PG_CONTROL_VERSION;
        ControlFile->catalog_version_no = CATALOG_VERSION_NO;
        ControlFile->blcksz = BLCKSZ;
        ControlFile->relseg_size = RELSEG_SIZE;
        ControlFile->xlog_seg_size = XLOG_SEG_SIZE;

        ControlFile->nameDataLen = NAMEDATALEN;
        ControlFile->funcMaxArgs = FUNC_MAX_ARGS;

#ifdef HAVE_INT64_TIMESTAMP
        ControlFile->enableIntTimes = TRUE;
#else
        ControlFile->enableIntTimes = FALSE;
#endif

        ControlFile->localeBuflen = LOCALE_NAME_BUFLEN;
        localeptr = setlocale(LC_COLLATE, NULL);
        if (!localeptr)
                ereport(PANIC,
                                (errmsg("invalid LC_COLLATE setting")));
        StrNCpy(ControlFile->lc_collate, localeptr, LOCALE_NAME_BUFLEN);
        localeptr = setlocale(LC_CTYPE, NULL);
        if (!localeptr)
                ereport(PANIC,
                                (errmsg("invalid LC_CTYPE setting")));
        StrNCpy(ControlFile->lc_ctype, localeptr, LOCALE_NAME_BUFLEN);

        /* Contents are protected with a CRC */
        INIT_CRC64(ControlFile->crc);
        COMP_CRC64(ControlFile->crc,
                           (char *) ControlFile + sizeof(crc64),
                           sizeof(ControlFileData) - sizeof(crc64));
        FIN_CRC64(ControlFile->crc);

        /*
         * We write out BLCKSZ bytes into pg_control, zero-padding the excess
         * over sizeof(ControlFileData).  This reduces the odds of
         * premature-EOF errors when reading pg_control.  We'll still fail
         * when we check the contents of the file, but hopefully with a more
         * specific error than "couldn't read pg_control".
         */
        if (sizeof(ControlFileData) > BLCKSZ)
                ereport(PANIC,
                                (errmsg("sizeof(ControlFileData) is larger than BLCKSZ; fix either one")));

        memset(buffer, 0, BLCKSZ);
        memcpy(buffer, ControlFile, sizeof(ControlFileData));

        fd = BasicOpenFile(ControlFilePath, O_RDWR | O_CREAT | O_EXCL | PG_BINARY,
                                           S_IRUSR | S_IWUSR);
        if (fd < 0)
                ereport(PANIC,
                                (errcode_for_file_access(),
                                 errmsg("could not create control file \"%s\": %m",
                                                ControlFilePath)));

        errno = 0;
        if (write(fd, buffer, BLCKSZ) != BLCKSZ)
        {
                /* if write didn't set errno, assume problem is no disk space */
                if (errno == 0)
                        errno = ENOSPC;
                ereport(PANIC,
                                (errcode_for_file_access(),
                                 errmsg("could not write to control file: %m")));
        }

        if (pg_fsync(fd) != 0)
                ereport(PANIC,
                                (errcode_for_file_access(),
                                 errmsg("could not fsync control file: %m")));

        if (close(fd))
                ereport(PANIC,
                                (errcode_for_file_access(),
                                 errmsg("could not close control file: %m")));
}

static void
ReadControlFile(void)
{
        crc64           crc;
        int                     fd;

        /*
         * Read data...
         */
        fd = BasicOpenFile(ControlFilePath, O_RDWR | PG_BINARY, S_IRUSR | S_IWUSR);
        if (fd < 0)
                ereport(PANIC,
                                (errcode_for_file_access(),
                                 errmsg("could not open control file \"%s\": %m",
                                                ControlFilePath)));

        if (read(fd, ControlFile, sizeof(ControlFileData)) != sizeof(ControlFileData))
                ereport(PANIC,
                                (errcode_for_file_access(),
                                 errmsg("could not read from control file: %m")));

        close(fd);

        /*
         * Check for expected pg_control format version.  If this is wrong,
         * the CRC check will likely fail because we'll be checking the wrong
         * number of bytes.  Complaining about wrong version will probably be
         * more enlightening than complaining about wrong CRC.
         */
        if (ControlFile->pg_control_version != PG_CONTROL_VERSION)
                ereport(FATAL,
                                (errmsg("database files are incompatible with server"),
                                 errdetail("The database cluster was initialized with PG_CONTROL_VERSION %d,"
                          " but the server was compiled with PG_CONTROL_VERSION %d.",
                                        ControlFile->pg_control_version, PG_CONTROL_VERSION),
                                 errhint("It looks like you need to initdb.")));
        /* Now check the CRC. */
        INIT_CRC64(crc);
        COMP_CRC64(crc,
                           (char *) ControlFile + sizeof(crc64),
                           sizeof(ControlFileData) - sizeof(crc64));
        FIN_CRC64(crc);

        if (!EQ_CRC64(crc, ControlFile->crc))
                ereport(FATAL,
                                (errmsg("incorrect checksum in control file")));

        /*
         * Do compatibility checking immediately.  We do this here for 2
         * reasons:
         *
         * (1) if the database isn't compatible with the backend executable, we
         * want to abort before we can possibly do any damage;
         *
         * (2) this code is executed in the postmaster, so the setlocale() will
         * propagate to forked backends, which aren't going to read this file
         * for themselves.      (These locale settings are considered critical
         * compatibility items because they can affect sort order of indexes.)
         */
        if (ControlFile->catalog_version_no != CATALOG_VERSION_NO)
                ereport(FATAL,
                                (errmsg("database files are incompatible with server"),
                                 errdetail("The database cluster was initialized with CATALOG_VERSION_NO %d,"
                          " but the server was compiled with CATALOG_VERSION_NO %d.",
                                        ControlFile->catalog_version_no, CATALOG_VERSION_NO),
                                 errhint("It looks like you need to initdb.")));
        if (ControlFile->blcksz != BLCKSZ)
                ereport(FATAL,
                                (errmsg("database files are incompatible with server"),
                 errdetail("The database cluster was initialized with BLCKSZ %d,"
                                   " but the server was compiled with BLCKSZ %d.",
                                   ControlFile->blcksz, BLCKSZ),
                         errhint("It looks like you need to recompile or initdb.")));
        if (ControlFile->relseg_size != RELSEG_SIZE)
                ereport(FATAL,
                                (errmsg("database files are incompatible with server"),
                                 errdetail("The database cluster was initialized with RELSEG_SIZE %d,"
                                         " but the server was compiled with RELSEG_SIZE %d.",
                                                   ControlFile->relseg_size, RELSEG_SIZE),
                         errhint("It looks like you need to recompile or initdb.")));
        if (ControlFile->xlog_seg_size != XLOG_SEG_SIZE)
                ereport(FATAL,
                                (errmsg("database files are incompatible with server"),
                                 errdetail("The database cluster was initialized with XLOG_SEG_SIZE %d,"
                                   " but the server was compiled with XLOG_SEG_SIZE %d.",
                                                   ControlFile->xlog_seg_size, XLOG_SEG_SIZE),
                         errhint("It looks like you need to recompile or initdb.")));
        if (ControlFile->nameDataLen != NAMEDATALEN)
                ereport(FATAL,
                                (errmsg("database files are incompatible with server"),
                                 errdetail("The database cluster was initialized with NAMEDATALEN %d,"
                                         " but the server was compiled with NAMEDATALEN %d.",
                                                   ControlFile->nameDataLen, NAMEDATALEN),
                         errhint("It looks like you need to recompile or initdb.")));
        if (ControlFile->funcMaxArgs != FUNC_MAX_ARGS)
                ereport(FATAL,
                                (errmsg("database files are incompatible with server"),
                                 errdetail("The database cluster was initialized with FUNC_MAX_ARGS %d,"
                                   " but the server was compiled with FUNC_MAX_ARGS %d.",
                                                   ControlFile->funcMaxArgs, FUNC_MAX_ARGS),
                         errhint("It looks like you need to recompile or initdb.")));

#ifdef HAVE_INT64_TIMESTAMP
        if (ControlFile->enableIntTimes != TRUE)
                ereport(FATAL,
                                (errmsg("database files are incompatible with server"),
                                 errdetail("The database cluster was initialized without HAVE_INT64_TIMESTAMP"
                          " but the server was compiled with HAVE_INT64_TIMESTAMP."),
                         errhint("It looks like you need to recompile or initdb.")));
#else
        if (ControlFile->enableIntTimes != FALSE)
                ereport(FATAL,
                                (errmsg("database files are incompatible with server"),
                                 errdetail("The database cluster was initialized with HAVE_INT64_TIMESTAMP"
                   " but the server was compiled without HAVE_INT64_TIMESTAMP."),
                         errhint("It looks like you need to recompile or initdb.")));
#endif

        if (ControlFile->localeBuflen != LOCALE_NAME_BUFLEN)
                ereport(FATAL,
                                (errmsg("database files are incompatible with server"),
                                 errdetail("The database cluster was initialized with LOCALE_NAME_BUFLEN %d,"
                          " but the server was compiled with LOCALE_NAME_BUFLEN %d.",
                                                   ControlFile->localeBuflen, LOCALE_NAME_BUFLEN),
                         errhint("It looks like you need to recompile or initdb.")));
        if (setlocale(LC_COLLATE, ControlFile->lc_collate) == NULL)
                ereport(FATAL,
                (errmsg("database files are incompatible with operating system"),
                 errdetail("The database cluster was initialized with LC_COLLATE \"%s\","
                                   " which is not recognized by setlocale().",
                                   ControlFile->lc_collate),
                 errhint("It looks like you need to initdb or install locale support.")));
        if (setlocale(LC_CTYPE, ControlFile->lc_ctype) == NULL)
                ereport(FATAL,
                (errmsg("database files are incompatible with operating system"),
                 errdetail("The database cluster was initialized with LC_CTYPE \"%s\","
                                   " which is not recognized by setlocale().",
                                   ControlFile->lc_ctype),
                 errhint("It looks like you need to initdb or install locale support.")));

        /* Make the fixed locale settings visible as GUC variables, too */
        SetConfigOption("lc_collate", ControlFile->lc_collate,
                                        PGC_INTERNAL, PGC_S_OVERRIDE);
        SetConfigOption("lc_ctype", ControlFile->lc_ctype,
                                        PGC_INTERNAL, PGC_S_OVERRIDE);
}

void
UpdateControlFile(void)
{
        int                     fd;

        INIT_CRC64(ControlFile->crc);
        COMP_CRC64(ControlFile->crc,
                           (char *) ControlFile + sizeof(crc64),
                           sizeof(ControlFileData) - sizeof(crc64));
        FIN_CRC64(ControlFile->crc);

        fd = BasicOpenFile(ControlFilePath, O_RDWR | PG_BINARY, S_IRUSR | S_IWUSR);
        if (fd < 0)
                ereport(PANIC,
                                (errcode_for_file_access(),
                                 errmsg("could not open control file \"%s\": %m",
                                                ControlFilePath)));

        errno = 0;
        if (write(fd, ControlFile, sizeof(ControlFileData)) != sizeof(ControlFileData))
        {
                /* if write didn't set errno, assume problem is no disk space */
                if (errno == 0)
                        errno = ENOSPC;
                ereport(PANIC,
                                (errcode_for_file_access(),
                                 errmsg("could not write to control file: %m")));
        }

        if (pg_fsync(fd) != 0)
                ereport(PANIC,
                                (errcode_for_file_access(),
                                 errmsg("could not fsync control file: %m")));

        if (close(fd))
                ereport(PANIC,
                                (errcode_for_file_access(),
                                 errmsg("could not close control file: %m")));
}

/*
 * Initialization of shared memory for XLOG
 */

int
XLOGShmemSize(void)
{
        if (XLOGbuffers < MinXLOGbuffers)
                XLOGbuffers = MinXLOGbuffers;

        return MAXALIGN(sizeof(XLogCtlData) + sizeof(XLogRecPtr) * XLOGbuffers)
                + BLCKSZ * XLOGbuffers +
                MAXALIGN(sizeof(ControlFileData));
}

void
XLOGShmemInit(void)
{
        bool            foundXLog,
                                foundCFile;

        /* this must agree with space requested by XLOGShmemSize() */
        if (XLOGbuffers < MinXLOGbuffers)
                XLOGbuffers = MinXLOGbuffers;

        XLogCtl = (XLogCtlData *)
                ShmemInitStruct("XLOG Ctl",
                                                MAXALIGN(sizeof(XLogCtlData) +
                                                                 sizeof(XLogRecPtr) * XLOGbuffers)
                                                + BLCKSZ * XLOGbuffers,
                                                &foundXLog);
        ControlFile = (ControlFileData *)
                ShmemInitStruct("Control File", sizeof(ControlFileData), &foundCFile);

        if (foundXLog || foundCFile)
        {
                /* both should be present or neither */
                Assert(foundXLog && foundCFile);
                return;
        }

        memset(XLogCtl, 0, sizeof(XLogCtlData));

        /*
         * Since XLogCtlData contains XLogRecPtr fields, its sizeof should be
         * a multiple of the alignment for same, so no extra alignment padding
         * is needed here.
         */
        XLogCtl->xlblocks = (XLogRecPtr *)
                (((char *) XLogCtl) + sizeof(XLogCtlData));
        memset(XLogCtl->xlblocks, 0, sizeof(XLogRecPtr) * XLOGbuffers);

        /*
         * Here, on the other hand, we must MAXALIGN to ensure the page
         * buffers have worst-case alignment.
         */
        XLogCtl->pages =
                ((char *) XLogCtl) + MAXALIGN(sizeof(XLogCtlData) +
                                                                          sizeof(XLogRecPtr) * XLOGbuffers);
        memset(XLogCtl->pages, 0, BLCKSZ * XLOGbuffers);

        /*
         * Do basic initialization of XLogCtl shared data. (StartupXLOG will
         * fill in additional info.)
         */
        XLogCtl->XLogCacheByte = BLCKSZ * XLOGbuffers;
        XLogCtl->XLogCacheBlck = XLOGbuffers - 1;
        XLogCtl->Insert.currpage = (XLogPageHeader) (XLogCtl->pages);
        SpinLockInit(&XLogCtl->info_lck);

        /*
         * If we are not in bootstrap mode, pg_control should already exist.
         * Read and validate it immediately (see comments in ReadControlFile()
         * for the reasons why).
         */
        if (!IsBootstrapProcessingMode())
                ReadControlFile();
}

/*
 * This func must be called ONCE on system install.  It creates pg_control
 * and the initial XLOG segment.
 */
void
BootStrapXLOG(void)
{
        CheckPoint      checkPoint;
        char       *buffer;
        XLogPageHeader page;
        XLogLongPageHeader longpage;
        XLogRecord *record;
        bool            use_existent;
        uint64          sysidentifier;
        struct timeval tv;
        crc64           crc;

        /*
         * Select a hopefully-unique system identifier code for this
         * installation. We use the result of gettimeofday(), including the
         * fractional seconds field, as being about as unique as we can easily
         * get.  (Think not to use random(), since it hasn't been seeded and
         * there's no portable way to seed it other than the system clock
         * value...)  The upper half of the uint64 value is just the tv_sec
         * part, while the lower half is the XOR of tv_sec and tv_usec.  This
         * is to ensure that we don't lose uniqueness unnecessarily if
         * "uint64" is really only 32 bits wide.  A person knowing this
         * encoding can determine the initialization time of the installation,
         * which could perhaps be useful sometimes.
         */
        gettimeofday(&tv, NULL);
        sysidentifier = ((uint64) tv.tv_sec) << 32;
        sysidentifier |= (uint32) (tv.tv_sec | tv.tv_usec);

        /* First timeline ID is always 1 */
        ThisTimeLineID = 1;

        /* Use malloc() to ensure buffer is MAXALIGNED */
        buffer = (char *) malloc(BLCKSZ);
        page = (XLogPageHeader) buffer;
        memset(buffer, 0, BLCKSZ);

        /* Set up information for the initial checkpoint record */
        checkPoint.redo.xlogid = 0;
        checkPoint.redo.xrecoff = SizeOfXLogLongPHD;
        checkPoint.undo = checkPoint.redo;
        checkPoint.ThisTimeLineID = ThisTimeLineID;
        checkPoint.nextXid = FirstNormalTransactionId;
        checkPoint.nextOid = BootstrapObjectIdData;
        checkPoint.time = time(NULL);

        ShmemVariableCache->nextXid = checkPoint.nextXid;
        ShmemVariableCache->nextOid = checkPoint.nextOid;
        ShmemVariableCache->oidCount = 0;

        /* Set up the XLOG page header */
        page->xlp_magic = XLOG_PAGE_MAGIC;
        page->xlp_info = XLP_LONG_HEADER;
        page->xlp_tli = ThisTimeLineID;
        page->xlp_pageaddr.xlogid = 0;
        page->xlp_pageaddr.xrecoff = 0;
        longpage = (XLogLongPageHeader) page;
        longpage->xlp_sysid = sysidentifier;
        longpage->xlp_seg_size = XLogSegSize;

        /* Insert the initial checkpoint record */
        record = (XLogRecord *) ((char *) page + SizeOfXLogLongPHD);
        record->xl_prev.xlogid = 0;
        record->xl_prev.xrecoff = 0;
        record->xl_xid = InvalidTransactionId;
        record->xl_len = sizeof(checkPoint);
        record->xl_info = XLOG_CHECKPOINT_SHUTDOWN;
        record->xl_rmid = RM_XLOG_ID;
        memcpy(XLogRecGetData(record), &checkPoint, sizeof(checkPoint));

        INIT_CRC64(crc);
        COMP_CRC64(crc, &checkPoint, sizeof(checkPoint));
        COMP_CRC64(crc, (char *) record + sizeof(crc64),
                           SizeOfXLogRecord - sizeof(crc64));
        FIN_CRC64(crc);
        record->xl_crc = crc;

        /* Create first XLOG segment file */
        use_existent = false;
        openLogFile = XLogFileInit(0, 0, &use_existent, false);

        /* Write the first page with the initial record */
        errno = 0;
        if (write(openLogFile, buffer, BLCKSZ) != BLCKSZ)
        {
                /* if write didn't set errno, assume problem is no disk space */
                if (errno == 0)
                        errno = ENOSPC;
                ereport(PANIC,
                                (errcode_for_file_access(),
                  errmsg("could not write bootstrap transaction log file: %m")));
        }

        if (pg_fsync(openLogFile) != 0)
                ereport(PANIC,
                                (errcode_for_file_access(),
                  errmsg("could not fsync bootstrap transaction log file: %m")));

        if (close(openLogFile))
                ereport(PANIC,
                                (errcode_for_file_access(),
                  errmsg("could not close bootstrap transaction log file: %m")));

        openLogFile = -1;

        /* Now create pg_control */

        memset(ControlFile, 0, sizeof(ControlFileData));
        /* Initialize pg_control status fields */
        ControlFile->system_identifier = sysidentifier;
        ControlFile->state = DB_SHUTDOWNED;
        ControlFile->time = checkPoint.time;
        ControlFile->logId = 0;
        ControlFile->logSeg = 1;
        ControlFile->checkPoint = checkPoint.redo;
        ControlFile->checkPointCopy = checkPoint;
        /* some additional ControlFile fields are set in WriteControlFile() */

        WriteControlFile();

        /* Bootstrap the commit log, too */
        BootStrapCLOG();
        BootStrapSUBTRANS();
}

static char *
str_time(time_t tnow)
{
        static char buf[128];

        strftime(buf, sizeof(buf),
                         "%Y-%m-%d %H:%M:%S %Z",
                         localtime(&tnow));

        return buf;
}

/*
 * See if there is a recovery command file (recovery.conf), and if so
 * read in parameters for archive recovery.
 *
 * XXX longer term intention is to expand this to
 * cater for additional parameters and controls
 * possibly use a flex lexer similar to the GUC one
 */
static void
readRecoveryCommandFile(void)
{
        char            recoveryCommandFile[MAXPGPATH];
        FILE       *fd;
        char            cmdline[MAXPGPATH];
        TimeLineID      rtli = 0;
        bool            rtliGiven = false;
        bool            syntaxError = false;

        snprintf(recoveryCommandFile, MAXPGPATH, "%s/recovery.conf", DataDir);
        fd = AllocateFile(recoveryCommandFile, "r");
        if (fd == NULL)
        {
                if (errno == ENOENT)
                        return;                         /* not there, so no archive recovery */
                ereport(FATAL,
                                (errcode_for_file_access(),
                                 errmsg("could not open recovery command file \"%s\": %m",
                                                recoveryCommandFile)));
        }

        ereport(LOG,
                        (errmsg("starting archive recovery")));

        /*
         * Parse the file...
         */
        while (fgets(cmdline, MAXPGPATH, fd) != NULL)
        {
                /* skip leading whitespace and check for # comment */
                char       *ptr;
                char       *tok1;
                char       *tok2;

                for (ptr = cmdline; *ptr; ptr++)
                {
                        if (!isspace((unsigned char) *ptr))
                                break;
                }
                if (*ptr == '\0' || *ptr == '#')
                        continue;

                /* identify the quoted parameter value */
                tok1 = strtok(ptr, "'");
                if (!tok1)
                {
                        syntaxError = true;
                        break;
                }
                tok2 = strtok(NULL, "'");
                if (!tok2)
                {
                        syntaxError = true;
                        break;
                }
                /* reparse to get just the parameter name */
                tok1 = strtok(ptr, " \t=");
                if (!tok1)
                {
                        syntaxError = true;
                        break;
                }

                if (strcmp(tok1, "restore_command") == 0)
                {
                        recoveryRestoreCommand = pstrdup(tok2);
                        ereport(LOG,
                                        (errmsg("restore_command = \"%s\"",
                                                        recoveryRestoreCommand)));
                }
                else if (strcmp(tok1, "recovery_target_timeline") == 0)
                {
                        rtliGiven = true;
                        if (strcmp(tok2, "latest") == 0)
                                rtli = 0;
                        else
                        {
                                errno = 0;
                                rtli = (TimeLineID) strtoul(tok2, NULL, 0);
                                if (errno == EINVAL || errno == ERANGE)
                                        ereport(FATAL,
                                                        (errmsg("recovery_target_timeline is not a valid number: \"%s\"",
                                                                        tok2)));
                        }
                        if (rtli)
                                ereport(LOG,
                                                (errmsg("recovery_target_timeline = %u", rtli)));
                        else
                                ereport(LOG,
                                                (errmsg("recovery_target_timeline = latest")));
                }
                else if (strcmp(tok1, "recovery_target_xid") == 0)
                {
                        errno = 0;
                        recoveryTargetXid = (TransactionId) strtoul(tok2, NULL, 0);
                        if (errno == EINVAL || errno == ERANGE)
                                ereport(FATAL,
                                                (errmsg("recovery_target_xid is not a valid number: \"%s\"",
                                                                tok2)));
                        ereport(LOG,
                                        (errmsg("recovery_target_xid = %u",
                                                        recoveryTargetXid)));
                        recoveryTarget = true;
                        recoveryTargetExact = true;
                }
                else if (strcmp(tok1, "recovery_target_time") == 0)
                {
                        /*
                         * if recovery_target_xid specified, then this overrides
                         * recovery_target_time
                         */
                        if (recoveryTargetExact)
                                continue;
                        recoveryTarget = true;
                        recoveryTargetExact = false;

                        /*
                         * Convert the time string given by the user to the time_t
                         * format. We use type abstime's input converter because we
                         * know abstime has the same representation as time_t.
                         */
                        recoveryTargetTime = (time_t)
                                DatumGetAbsoluteTime(DirectFunctionCall1(abstimein,
                                                                                                 CStringGetDatum(tok2)));
                        ereport(LOG,
                                        (errmsg("recovery_target_time = %s",
                                                  DatumGetCString(DirectFunctionCall1(abstimeout,
                        AbsoluteTimeGetDatum((AbsoluteTime) recoveryTargetTime))))));
                }
                else if (strcmp(tok1, "recovery_target_inclusive") == 0)
                {
                        /*
                         * does nothing if a recovery_target is not also set
                         */
                        if (strcmp(tok2, "true") == 0)
                                recoveryTargetInclusive = true;
                        else
                        {
                                recoveryTargetInclusive = false;
                                tok2 = "false";
                        }
                        ereport(LOG,
                                        (errmsg("recovery_target_inclusive = %s", tok2)));
                }
                else
                        ereport(FATAL,
                                        (errmsg("unrecognized recovery parameter \"%s\"",
                                                        tok1)));
        }

        FreeFile(fd);

        if (syntaxError)
                ereport(FATAL,
                                (errmsg("syntax error in recovery command file: %s",
                                                cmdline),
                  errhint("Lines should have the format parameter = 'value'.")));

        /* Check that required parameters were supplied */
        if (recoveryRestoreCommand == NULL)
                ereport(FATAL,
                                (errmsg("recovery command file \"%s\" did not specify restore_command",
                                                recoveryCommandFile)));

        /* Enable fetching from archive recovery area */
        InArchiveRecovery = true;

        /*
         * If user specified recovery_target_timeline, validate it or compute
         * the "latest" value.  We can't do this until after we've gotten the
         * restore command and set InArchiveRecovery, because we need to fetch
         * timeline history files from the archive.
         */
        if (rtliGiven)
        {
                if (rtli)
                {
                        /* Timeline 1 does not have a history file, all else should */
                        if (rtli != 1 && !existsTimeLineHistory(rtli))
                                ereport(FATAL,
                                        (errmsg("recovery_target_timeline %u does not exist",
                                                        rtli)));
                        recoveryTargetTLI = rtli;
                }
                else
                {
                        /* We start the "latest" search from pg_control's timeline */
                        recoveryTargetTLI = findNewestTimeLine(recoveryTargetTLI);
                }
        }
}

/*
 * Exit archive-recovery state
 */
static void
exitArchiveRecovery(TimeLineID endTLI, uint32 endLogId, uint32 endLogSeg)
{
        char            recoveryPath[MAXPGPATH];
        char            xlogpath[MAXPGPATH];
        char            recoveryCommandFile[MAXPGPATH];
        char            recoveryCommandDone[MAXPGPATH];

        /*
         * We are no longer in archive recovery state.
         */
        InArchiveRecovery = false;

        /*
         * We should have the ending log segment currently open.  Verify, and
         * then close it (to avoid problems on Windows with trying to rename
         * or delete an open file).
         */
        Assert(readFile >= 0);
        Assert(readId == endLogId);
        Assert(readSeg == endLogSeg);

        close(readFile);
        readFile = -1;

        /*
         * If the segment was fetched from archival storage, we want to
         * replace the existing xlog segment (if any) with the archival
         * version.  This is because whatever is in XLogDir is very possibly
         * older than what we have from the archives, since it could have come
         * from restoring a PGDATA backup.      In any case, the archival version
         * certainly is more descriptive of what our current database state
         * is, because that is what we replayed from.
         *
         * Note that if we are establishing a new timeline, ThisTimeLineID is
         * already set to the new value, and so we will create a new file
         * instead of overwriting any existing file.
         */
        snprintf(recoveryPath, MAXPGPATH, "%s/RECOVERYXLOG", XLogDir);
        XLogFilePath(xlogpath, ThisTimeLineID, endLogId, endLogSeg);

        if (restoredFromArchive)
        {
                ereport(DEBUG3,
                                (errmsg_internal("moving last restored xlog to \"%s\"",
                                                                 xlogpath)));
                unlink(xlogpath);               /* might or might not exist */
                if (rename(recoveryPath, xlogpath) != 0)
                        ereport(FATAL,
                                        (errcode_for_file_access(),
                                         errmsg("could not rename file \"%s\" to \"%s\": %m",
                                                        recoveryPath, xlogpath)));
                /* XXX might we need to fix permissions on the file? */
        }
        else
        {
                /*
                 * If the latest segment is not archival, but there's still a
                 * RECOVERYXLOG laying about, get rid of it.
                 */
                unlink(recoveryPath);   /* ignore any error */

                /*
                 * If we are establishing a new timeline, we have to copy data
                 * from the last WAL segment of the old timeline to create a
                 * starting WAL segment for the new timeline.
                 */
                if (endTLI != ThisTimeLineID)
                        XLogFileCopy(endLogId, endLogSeg,
                                                 endTLI, endLogId, endLogSeg);
        }

        /*
         * Let's just make real sure there are not .ready or .done flags
         * posted for the new segment.
         */
        XLogFileName(xlogpath, ThisTimeLineID, endLogId, endLogSeg);
        XLogArchiveCleanup(xlogpath);

        /* Get rid of any remaining recovered timeline-history file, too */
        snprintf(recoveryPath, MAXPGPATH, "%s/RECOVERYHISTORY", XLogDir);
        unlink(recoveryPath);           /* ignore any error */

        /*
         * Rename the config file out of the way, so that we don't
         * accidentally re-enter archive recovery mode in a subsequent crash.
         */
        snprintf(recoveryCommandFile, MAXPGPATH, "%s/recovery.conf", DataDir);
        snprintf(recoveryCommandDone, MAXPGPATH, "%s/recovery.done", DataDir);
        unlink(recoveryCommandDone);
        if (rename(recoveryCommandFile, recoveryCommandDone) != 0)
                ereport(FATAL,
                                (errcode_for_file_access(),
                                 errmsg("could not rename file \"%s\" to \"%s\": %m",
                                                recoveryCommandFile, recoveryCommandDone)));

        ereport(LOG,
                        (errmsg("archive recovery complete")));
}

/*
 * For point-in-time recovery, this function decides whether we want to
 * stop applying the XLOG at or after the current record.
 *
 * Returns TRUE if we are stopping, FALSE otherwise.  On TRUE return,
 * *includeThis is set TRUE if we should apply this record before stopping.
 * Also, some information is saved in recoveryStopXid et al for use in
 * annotating the new timeline's history file.
 */
static bool
recoveryStopsHere(XLogRecord *record, bool *includeThis)
{
        bool            stopsHere;
        uint8           record_info;
        time_t          recordXtime;

        /* Do we have a PITR target at all? */
        if (!recoveryTarget)
                return false;

        /* We only consider stopping at COMMIT or ABORT records */
        if (record->xl_rmid != RM_XACT_ID)
                return false;
        record_info = record->xl_info & ~XLR_INFO_MASK;
        if (record_info == XLOG_XACT_COMMIT)
        {
                xl_xact_commit *recordXactCommitData;

                recordXactCommitData = (xl_xact_commit *) XLogRecGetData(record);
                recordXtime = recordXactCommitData->xtime;
        }
        else if (record_info == XLOG_XACT_ABORT)
        {
                xl_xact_abort *recordXactAbortData;

                recordXactAbortData = (xl_xact_abort *) XLogRecGetData(record);
                recordXtime = recordXactAbortData->xtime;
        }
        else
                return false;

        if (recoveryTargetExact)
        {
                /*
                 * there can be only one transaction end record with this exact
                 * transactionid
                 *
                 * when testing for an xid, we MUST test for equality only, since
                 * transactions are numbered in the order they start, not the
                 * order they complete. A higher numbered xid will complete before
                 * you about 50% of the time...
                 */
                stopsHere = (record->xl_xid == recoveryTargetXid);
                if (stopsHere)
                        *includeThis = recoveryTargetInclusive;
        }
        else
        {
                /*
                 * there can be many transactions that share the same commit time,
                 * so we stop after the last one, if we are inclusive, or stop at
                 * the first one if we are exclusive
                 */
                if (recoveryTargetInclusive)
                        stopsHere = (recordXtime > recoveryTargetTime);
                else
                        stopsHere = (recordXtime >= recoveryTargetTime);
                if (stopsHere)
                        *includeThis = false;
        }

        if (stopsHere)
        {
                recoveryStopXid = record->xl_xid;
                recoveryStopTime = recordXtime;
                recoveryStopAfter = *includeThis;

                if (record_info == XLOG_XACT_COMMIT)
                {
                        if (recoveryStopAfter)
                                ereport(LOG,
                                                (errmsg("recovery stopping after commit of transaction %u, time %s",
                                                  recoveryStopXid, str_time(recoveryStopTime))));
                        else
                                ereport(LOG,
                                                (errmsg("recovery stopping before commit of transaction %u, time %s",
                                                  recoveryStopXid, str_time(recoveryStopTime))));
                }
                else
                {
                        if (recoveryStopAfter)
                                ereport(LOG,
                                                (errmsg("recovery stopping after abort of transaction %u, time %s",
                                                  recoveryStopXid, str_time(recoveryStopTime))));
                        else
                                ereport(LOG,
                                                (errmsg("recovery stopping before abort of transaction %u, time %s",
                                                  recoveryStopXid, str_time(recoveryStopTime))));
                }
        }

        return stopsHere;
}

/*
 * This must be called ONCE during postmaster or standalone-backend startup
 */
void
StartupXLOG(void)
{
        XLogCtlInsert *Insert;
        CheckPoint      checkPoint;
        bool            wasShutdown;
        bool            needNewTimeLine = false;
        XLogRecPtr      RecPtr,
                                LastRec,
                                checkPointLoc,
                                EndOfLog;
        uint32          endLogId;
        uint32          endLogSeg;
        XLogRecord *record;
        uint32          freespace;

        CritSectionCount++;

        /*
         * Read control file and check XLOG status looks valid.
         *
         * Note: in most control paths, *ControlFile is already valid and we need
         * not do ReadControlFile() here, but might as well do it to be sure.
         */
        ReadControlFile();

        if (ControlFile->logSeg == 0 ||
                ControlFile->state < DB_SHUTDOWNED ||
                ControlFile->state > DB_IN_PRODUCTION ||
                !XRecOffIsValid(ControlFile->checkPoint.xrecoff))
                ereport(FATAL,
                                (errmsg("control file contains invalid data")));

        if (ControlFile->state == DB_SHUTDOWNED)
                ereport(LOG,
                                (errmsg("database system was shut down at %s",
                                                str_time(ControlFile->time))));
        else if (ControlFile->state == DB_SHUTDOWNING)
                ereport(LOG,
                                (errmsg("database system shutdown was interrupted at %s",
                                                str_time(ControlFile->time))));
        else if (ControlFile->state == DB_IN_RECOVERY)
                ereport(LOG,
                (errmsg("database system was interrupted while in recovery at %s",
                                str_time(ControlFile->time)),
                 errhint("This probably means that some data is corrupted and"
                                 " you will have to use the last backup for recovery.")));
        else if (ControlFile->state == DB_IN_PRODUCTION)
                ereport(LOG,
                                (errmsg("database system was interrupted at %s",
                                                str_time(ControlFile->time))));

        /* This is just to allow attaching to startup process with a debugger */
#ifdef XLOG_REPLAY_DELAY
        if (ControlFile->state != DB_SHUTDOWNED)
                pg_usleep(60000000L);
#endif

        /*
         * Initialize on the assumption we want to recover to the same
         * timeline that's active according to pg_control.
         */
        recoveryTargetTLI = ControlFile->checkPointCopy.ThisTimeLineID;

        /*
         * Check for recovery control file, and if so set up state for offline
         * recovery
         */
        readRecoveryCommandFile();

        /* Now we can determine the list of expected TLIs */
        expectedTLIs = readTimeLineHistory(recoveryTargetTLI);

        /*
         * If pg_control's timeline is not in expectedTLIs, then we cannot
         * proceed: the backup is not part of the history of the requested
         * timeline.
         */
        if (!list_member_int(expectedTLIs,
                                           (int) ControlFile->checkPointCopy.ThisTimeLineID))
                ereport(FATAL,
                                (errmsg("requested timeline %u is not a child of database system timeline %u",
                                                recoveryTargetTLI,
                                                ControlFile->checkPointCopy.ThisTimeLineID)));

        if (read_backup_label(&checkPointLoc))
        {
                /*
                 * When a backup_label file is present, we want to roll forward
                 * from the checkpoint it identifies, rather than using
                 * pg_control.
                 */
                record = ReadCheckpointRecord(checkPointLoc, 0);
                if (record != NULL)
                {
                        ereport(LOG,
                                        (errmsg("checkpoint record is at %X/%X",
                                                  checkPointLoc.xlogid, checkPointLoc.xrecoff)));
                        InRecovery = true;      /* force recovery even if SHUTDOWNED */
                }
                else
                {
                        ereport(PANIC,
                                  (errmsg("could not locate required checkpoint record"),
                                   errhint("If you are not restoring from a backup, try removing $PGDATA/backup_label.")));
                }
        }
        else
        {
                /*
                 * Get the last valid checkpoint record.  If the latest one
                 * according to pg_control is broken, try the next-to-last one.
                 */
                checkPointLoc = ControlFile->checkPoint;
                record = ReadCheckpointRecord(checkPointLoc, 1);
                if (record != NULL)
                {
                        ereport(LOG,
                                        (errmsg("checkpoint record is at %X/%X",
                                                  checkPointLoc.xlogid, checkPointLoc.xrecoff)));
                }
                else
                {
                        checkPointLoc = ControlFile->prevCheckPoint;
                        record = ReadCheckpointRecord(checkPointLoc, 2);
                        if (record != NULL)
                        {
                                ereport(LOG,
                                         (errmsg("using previous checkpoint record at %X/%X",
                                                  checkPointLoc.xlogid, checkPointLoc.xrecoff)));
                                InRecovery = true;              /* force recovery even if
                                                                                 * SHUTDOWNED */
                        }
                        else
                                ereport(PANIC,
                                 (errmsg("could not locate a valid checkpoint record")));
                }
        }

        LastRec = RecPtr = checkPointLoc;
        memcpy(&checkPoint, XLogRecGetData(record), sizeof(CheckPoint));
        wasShutdown = (record->xl_info == XLOG_CHECKPOINT_SHUTDOWN);

        ereport(LOG,
                        (errmsg("redo record is at %X/%X; undo record is at %X/%X; shutdown %s",
                                        checkPoint.redo.xlogid, checkPoint.redo.xrecoff,
                                        checkPoint.undo.xlogid, checkPoint.undo.xrecoff,
                                        wasShutdown ? "TRUE" : "FALSE")));
        ereport(LOG,
                        (errmsg("next transaction ID: %u; next OID: %u",
                                        checkPoint.nextXid, checkPoint.nextOid)));
        if (!TransactionIdIsNormal(checkPoint.nextXid))
                ereport(PANIC,
                                (errmsg("invalid next transaction ID")));

        ShmemVariableCache->nextXid = checkPoint.nextXid;
        ShmemVariableCache->nextOid = checkPoint.nextOid;
        ShmemVariableCache->oidCount = 0;

        /*
         * We must replay WAL entries using the same TimeLineID they were
         * created under, so temporarily adopt the TLI indicated by the
         * checkpoint (see also xlog_redo()).
         */
        ThisTimeLineID = checkPoint.ThisTimeLineID;

        RedoRecPtr = XLogCtl->Insert.RedoRecPtr = checkPoint.redo;

        if (XLByteLT(RecPtr, checkPoint.redo))
                ereport(PANIC,
                                (errmsg("invalid redo in checkpoint record")));
        if (checkPoint.undo.xrecoff == 0)
                checkPoint.undo = RecPtr;

        /*
         * Check whether we need to force recovery from WAL.  If it appears to
         * have been a clean shutdown and we did not have a recovery.conf
         * file, then assume no recovery needed.
         */
        if (XLByteLT(checkPoint.undo, RecPtr) ||
                XLByteLT(checkPoint.redo, RecPtr))
        {
                if (wasShutdown)
                        ereport(PANIC,
                        (errmsg("invalid redo/undo record in shutdown checkpoint")));
                InRecovery = true;
        }
        else if (ControlFile->state != DB_SHUTDOWNED)
                InRecovery = true;
        else if (InArchiveRecovery)
        {
                /* force recovery due to presence of recovery.conf */
                InRecovery = true;
        }

        /* REDO */
        if (InRecovery)
        {
                int                     rmid;

                if (InArchiveRecovery)
                        ereport(LOG,
                                        (errmsg("automatic recovery in progress")));
                else
                        ereport(LOG,
                                        (errmsg("database system was not properly shut down; "
                                                        "automatic recovery in progress")));
                ControlFile->state = DB_IN_RECOVERY;
                ControlFile->time = time(NULL);
                UpdateControlFile();

                /* Start up the recovery environment */
                XLogInitRelationCache();

                for (rmid = 0; rmid <= RM_MAX_ID; rmid++)
                {
                        if (RmgrTable[rmid].rm_startup != NULL)
                                RmgrTable[rmid].rm_startup();
                }

                /*
                 * Find the first record that logically follows the checkpoint ---
                 * it might physically precede it, though.
                 */
                if (XLByteLT(checkPoint.redo, RecPtr))
                {
                        /* back up to find the record */
                        record = ReadRecord(&(checkPoint.redo), PANIC);
                }
                else
                {
                        /* just have to read next record after CheckPoint */
                        record = ReadRecord(NULL, LOG);
                }

                if (record != NULL)
                {
                        bool            recoveryContinue = true;
                        bool            recoveryApply = true;

                        InRedo = true;
                        ereport(LOG,
                                        (errmsg("redo starts at %X/%X",
                                                        ReadRecPtr.xlogid, ReadRecPtr.xrecoff)));

                        /*
                         * main redo apply loop
                         */
                        do
                        {
#ifdef WAL_DEBUG
                                if (XLOG_DEBUG)
                                {
                                        char            buf[8192];

                                        sprintf(buf, "REDO @ %X/%X; LSN %X/%X: ",
                                                        ReadRecPtr.xlogid, ReadRecPtr.xrecoff,
                                                        EndRecPtr.xlogid, EndRecPtr.xrecoff);
                                        xlog_outrec(buf, record);
                                        strcat(buf, " - ");
                                        RmgrTable[record->xl_rmid].rm_desc(buf,
                                                                record->xl_info, XLogRecGetData(record));
                                        elog(LOG, "%s", buf);
                                }
#endif

                                /*
                                 * Have we reached our recovery target?
                                 */
                                if (recoveryStopsHere(record, &recoveryApply))
                                {
                                        needNewTimeLine = true;         /* see below */
                                        recoveryContinue = false;
                                        if (!recoveryApply)
                                                break;
                                }

                                /* nextXid must be beyond record's xid */
                                if (TransactionIdFollowsOrEquals(record->xl_xid,
                                                                                        ShmemVariableCache->nextXid))
                                {
                                        ShmemVariableCache->nextXid = record->xl_xid;
                                        TransactionIdAdvance(ShmemVariableCache->nextXid);
                                }

                                if (record->xl_info & XLR_BKP_BLOCK_MASK)
                                        RestoreBkpBlocks(record, EndRecPtr);

                                RmgrTable[record->xl_rmid].rm_redo(EndRecPtr, record);

                                LastRec = ReadRecPtr;

                                record = ReadRecord(NULL, LOG);
                        } while (record != NULL && recoveryContinue);

                        /*
                         * end of main redo apply loop
                         */

                        ereport(LOG,
                                        (errmsg("redo done at %X/%X",
                                                        ReadRecPtr.xlogid, ReadRecPtr.xrecoff)));
                        InRedo = false;
                }
                else
                {
                        /* there are no WAL records following the checkpoint */
                        ereport(LOG,
                                        (errmsg("redo is not required")));
                }
        }

        /*
         * Re-fetch the last valid or last applied record, so we can identify
         * the exact endpoint of what we consider the valid portion of WAL.
         */
        record = ReadRecord(&LastRec, PANIC);
        EndOfLog = EndRecPtr;
        XLByteToPrevSeg(EndOfLog, endLogId, endLogSeg);

        /*
         * Complain if we did not roll forward far enough to render the backup
         * dump consistent.
         */
        if (XLByteLT(EndOfLog, recoveryMinXlogOffset))
        {
                if (needNewTimeLine)    /* stopped because of stop request */
                        ereport(FATAL,
                                        (errmsg("requested recovery stop point is before end time of backup dump")));
                else
                        /* ran off end of WAL */
                        ereport(FATAL,
                                        (errmsg("WAL ends before end time of backup dump")));
        }

        /*
         * Consider whether we need to assign a new timeline ID.
         *
         * If we stopped short of the end of WAL during recovery, then we are
         * generating a new timeline and must assign it a unique new ID.
         * Otherwise, we can just extend the timeline we were in when we ran
         * out of WAL.
         */
        if (needNewTimeLine)
        {
                ThisTimeLineID = findNewestTimeLine(recoveryTargetTLI) + 1;
                ereport(LOG,
                                (errmsg("selected new timeline ID: %u", ThisTimeLineID)));
                writeTimeLineHistory(ThisTimeLineID, recoveryTargetTLI,
                                                         curFileTLI, endLogId, endLogSeg);
        }

        /* Save the selected TimeLineID in shared memory, too */
        XLogCtl->ThisTimeLineID = ThisTimeLineID;

        /*
         * We are now done reading the old WAL.  Turn off archive fetching if
         * it was active, and make a writable copy of the last WAL segment.
         * (Note that we also have a copy of the last block of the old WAL in
         * readBuf; we will use that below.)
         */
        if (InArchiveRecovery)
                exitArchiveRecovery(curFileTLI, endLogId, endLogSeg);

        /*
         * Prepare to write WAL starting at EndOfLog position, and init xlog
         * buffer cache using the block containing the last record from the
         * previous incarnation.
         */
        openLogId = endLogId;
        openLogSeg = endLogSeg;
        openLogFile = XLogFileOpen(openLogId, openLogSeg);
        openLogOff = 0;
        ControlFile->logId = openLogId;
        ControlFile->logSeg = openLogSeg + 1;
        Insert = &XLogCtl->Insert;
        Insert->PrevRecord = LastRec;
        XLogCtl->xlblocks[0].xlogid = openLogId;
        XLogCtl->xlblocks[0].xrecoff =
                ((EndOfLog.xrecoff - 1) / BLCKSZ + 1) * BLCKSZ;

        /*
         * Tricky point here: readBuf contains the *last* block that the
         * LastRec record spans, not the one it starts in.      The last block is
         * indeed the one we want to use.
         */
        Assert(readOff == (XLogCtl->xlblocks[0].xrecoff - BLCKSZ) % XLogSegSize);
        memcpy((char *) Insert->currpage, readBuf, BLCKSZ);
        Insert->currpos = (char *) Insert->currpage +
                (EndOfLog.xrecoff + BLCKSZ - XLogCtl->xlblocks[0].xrecoff);

        LogwrtResult.Write = LogwrtResult.Flush = EndOfLog;

        XLogCtl->Write.LogwrtResult = LogwrtResult;
        Insert->LogwrtResult = LogwrtResult;
        XLogCtl->LogwrtResult = LogwrtResult;

        XLogCtl->LogwrtRqst.Write = EndOfLog;
        XLogCtl->LogwrtRqst.Flush = EndOfLog;

        freespace = INSERT_FREESPACE(Insert);
        if (freespace > 0)
        {
                /* Make sure rest of page is zero */
                MemSet(Insert->currpos, 0, freespace);
                XLogCtl->Write.curridx = 0;
        }
        else
        {
                /*
                 * Whenever Write.LogwrtResult points to exactly the end of a
                 * page, Write.curridx must point to the *next* page (see
                 * XLogWrite()).
                 *
                 * Note: it might seem we should do AdvanceXLInsertBuffer() here, but
                 * this is sufficient.  The first actual attempt to insert a log
                 * record will advance the insert state.
                 */
                XLogCtl->Write.curridx = NextBufIdx(0);
        }

#ifdef NOT_USED
        /* UNDO */
        if (InRecovery)
        {
                RecPtr = ReadRecPtr;
                if (XLByteLT(checkPoint.undo, RecPtr))
                {
                        ereport(LOG,
                                        (errmsg("undo starts at %X/%X",
                                                        RecPtr.xlogid, RecPtr.xrecoff)));
                        do
                        {
                                record = ReadRecord(&RecPtr, PANIC);
                                if (TransactionIdIsValid(record->xl_xid) &&
                                        !TransactionIdDidCommit(record->xl_xid))
                                        RmgrTable[record->xl_rmid].rm_undo(EndRecPtr, record);
                                RecPtr = record->xl_prev;
                        } while (XLByteLE(checkPoint.undo, RecPtr));
                        ereport(LOG,
                                        (errmsg("undo done at %X/%X",
                                                        ReadRecPtr.xlogid, ReadRecPtr.xrecoff)));
                }
                else
                        ereport(LOG,
                                        (errmsg("undo is not required")));
        }
#endif

        if (InRecovery)
        {
                int                     rmid;

                /*
                 * Allow resource managers to do any required cleanup.
                 */
                for (rmid = 0; rmid <= RM_MAX_ID; rmid++)
                {
                        if (RmgrTable[rmid].rm_cleanup != NULL)
                                RmgrTable[rmid].rm_cleanup();
                }

                /*
                 * Perform a new checkpoint to update our recovery activity to
                 * disk.
                 *
                 * Note that we write a shutdown checkpoint rather than an on-line
                 * one.  This is not particularly critical, but since we may be
                 * assigning a new TLI, using a shutdown checkpoint allows us to
                 * have the rule that TLI only changes in shutdown checkpoints,
                 * which allows some extra error checking in xlog_redo.
                 *
                 * In case we had to use the secondary checkpoint, make sure that it
                 * will still be shown as the secondary checkpoint after this
                 * CreateCheckPoint operation; we don't want the broken primary
                 * checkpoint to become prevCheckPoint...
                 */
                if (XLByteEQ(checkPointLoc, ControlFile->prevCheckPoint))
                        ControlFile->checkPoint = checkPointLoc;

                CreateCheckPoint(true, true);

                /*
                 * Close down recovery environment
                 */
                XLogCloseRelationCache();

                /*
                 * Now that we've checkpointed the recovery, it's safe to flush
                 * old backup_label, if present.
                 */
                remove_backup_label();
        }

        /*
         * Preallocate additional log files, if wanted.
         */
        PreallocXlogFiles(EndOfLog);

        /*
         * Okay, we're officially UP.
         */
        InRecovery = false;

        ControlFile->state = DB_IN_PRODUCTION;
        ControlFile->time = time(NULL);
        UpdateControlFile();

        /* Start up the commit log, too */
        StartupCLOG();
        StartupSUBTRANS();

        ereport(LOG,
                        (errmsg("database system is ready")));
        CritSectionCount--;

        /* Shut down readFile facility, free space */
        if (readFile >= 0)
        {
                close(readFile);
                readFile = -1;
        }
        if (readBuf)
        {
                free(readBuf);
                readBuf = NULL;
        }
        if (readRecordBuf)
        {
                free(readRecordBuf);
                readRecordBuf = NULL;
                readRecordBufSize = 0;
        }
}

/*
 * Subroutine to try to fetch and validate a prior checkpoint record.
 *
 * whichChkpt identifies the checkpoint (merely for reporting purposes).
 * 1 for "primary", 2 for "secondary", 0 for "other" (backup_label)
 */
static XLogRecord *
ReadCheckpointRecord(XLogRecPtr RecPtr, int whichChkpt)
{
        XLogRecord *record;

        if (!XRecOffIsValid(RecPtr.xrecoff))
        {
                switch (whichChkpt)
                {
                        case 1:
                                ereport(LOG,
                                                (errmsg("invalid primary checkpoint link in control file")));
                                break;
                        case 2:
                                ereport(LOG,
                                                (errmsg("invalid secondary checkpoint link in control file")));
                                break;
                        default:
                                ereport(LOG,
                                (errmsg("invalid checkpoint link in backup_label file")));
                                break;
                }
                return NULL;
        }

        record = ReadRecord(&RecPtr, LOG);

        if (record == NULL)
        {
                switch (whichChkpt)
                {
                        case 1:
                                ereport(LOG,
                                                (errmsg("invalid primary checkpoint record")));
                                break;
                        case 2:
                                ereport(LOG,
                                                (errmsg("invalid secondary checkpoint record")));
                                break;
                        default:
                                ereport(LOG,
                                                (errmsg("invalid checkpoint record")));
                                break;
                }
                return NULL;
        }
        if (record->xl_rmid != RM_XLOG_ID)
        {
                switch (whichChkpt)
                {
                        case 1:
                                ereport(LOG,
                                                (errmsg("invalid resource manager ID in primary checkpoint record")));
                                break;
                        case 2:
                                ereport(LOG,
                                                (errmsg("invalid resource manager ID in secondary checkpoint record")));
                                break;
                        default:
                                ereport(LOG,
                                                (errmsg("invalid resource manager ID in checkpoint record")));
                                break;
                }
                return NULL;
        }
        if (record->xl_info != XLOG_CHECKPOINT_SHUTDOWN &&
                record->xl_info != XLOG_CHECKPOINT_ONLINE)
        {
                switch (whichChkpt)
                {
                        case 1:
                                ereport(LOG,
                                (errmsg("invalid xl_info in primary checkpoint record")));
                                break;
                        case 2:
                                ereport(LOG,
                                                (errmsg("invalid xl_info in secondary checkpoint record")));
                                break;
                        default:
                                ereport(LOG,
                                                (errmsg("invalid xl_info in checkpoint record")));
                                break;
                }
                return NULL;
        }
        if (record->xl_len != sizeof(CheckPoint))
        {
                switch (whichChkpt)
                {
                        case 1:
                                ereport(LOG,
                                (errmsg("invalid length of primary checkpoint record")));
                                break;
                        case 2:
                                ereport(LOG,
                                                (errmsg("invalid length of secondary checkpoint record")));
                                break;
                        default:
                                ereport(LOG,
                                                (errmsg("invalid length of checkpoint record")));
                                break;
                }
                return NULL;
        }
        return record;
}

/*
 * This must be called during startup of a backend process, except that
 * it need not be called in a standalone backend (which does StartupXLOG
 * instead).  We need to initialize the local copies of ThisTimeLineID and
 * RedoRecPtr.
 *
 * Note: before Postgres 8.0, we went to some effort to keep the postmaster
 * process's copies of ThisTimeLineID and RedoRecPtr valid too.  This was
 * unnecessary however, since the postmaster itself never touches XLOG anyway.
 */
void
InitXLOGAccess(void)
{
        /* ThisTimeLineID doesn't change so we need no lock to copy it */
        ThisTimeLineID = XLogCtl->ThisTimeLineID;
        /* Use GetRedoRecPtr to copy the RedoRecPtr safely */
        (void) GetRedoRecPtr();
}

/*
 * Once spawned, a backend may update its local RedoRecPtr from
 * XLogCtl->Insert.RedoRecPtr; it must hold the insert lock or info_lck
 * to do so.  This is done in XLogInsert() or GetRedoRecPtr().
 */
XLogRecPtr
GetRedoRecPtr(void)
{
        /* use volatile pointer to prevent code rearrangement */
        volatile XLogCtlData *xlogctl = XLogCtl;

        SpinLockAcquire_NoHoldoff(&xlogctl->info_lck);
        Assert(XLByteLE(RedoRecPtr, xlogctl->Insert.RedoRecPtr));
        RedoRecPtr = xlogctl->Insert.RedoRecPtr;
        SpinLockRelease_NoHoldoff(&xlogctl->info_lck);

        return RedoRecPtr;
}

/*
 * This must be called ONCE during postmaster or standalone-backend shutdown
 */
void
ShutdownXLOG(int code, Datum arg)
{
        ereport(LOG,
                        (errmsg("shutting down")));

        CritSectionCount++;
        CreateCheckPoint(true, true);
        ShutdownCLOG();
        ShutdownSUBTRANS();
        CritSectionCount--;

        ereport(LOG,
                        (errmsg("database system is shut down")));
}

/*
 * Perform a checkpoint --- either during shutdown, or on-the-fly
 *
 * If force is true, we force a checkpoint regardless of whether any XLOG
 * activity has occurred since the last one.
 */
void
CreateCheckPoint(bool shutdown, bool force)
{
        CheckPoint      checkPoint;
        XLogRecPtr      recptr;
        XLogCtlInsert *Insert = &XLogCtl->Insert;
        XLogRecData rdata;
        uint32          freespace;
        uint32          _logId;
        uint32          _logSeg;

        /*
         * Acquire CheckpointLock to ensure only one checkpoint happens at a
         * time.  (This is just pro forma, since in the present system
         * structure there is only one process that is allowed to issue
         * checkpoints at any given time.)
         */
        LWLockAcquire(CheckpointLock, LW_EXCLUSIVE);

        /*
         * Use a critical section to force system panic if we have trouble.
         */
        START_CRIT_SECTION();

        if (shutdown)
        {
                ControlFile->state = DB_SHUTDOWNING;
                ControlFile->time = time(NULL);
                UpdateControlFile();
        }

        MemSet(&checkPoint, 0, sizeof(checkPoint));
        checkPoint.ThisTimeLineID = ThisTimeLineID;
        checkPoint.time = time(NULL);

        /*
         * We must hold CheckpointStartLock while determining the checkpoint
         * REDO pointer.  This ensures that any concurrent transaction commits
         * will be either not yet logged, or logged and recorded in pg_clog.
         * See notes in RecordTransactionCommit().
         */
        LWLockAcquire(CheckpointStartLock, LW_EXCLUSIVE);

        /* And we need WALInsertLock too */
        LWLockAcquire(WALInsertLock, LW_EXCLUSIVE);

        /*
         * If this isn't a shutdown or forced checkpoint, and we have not
         * inserted any XLOG records since the start of the last checkpoint,
         * skip the checkpoint.  The idea here is to avoid inserting duplicate
         * checkpoints when the system is idle. That wastes log space, and
         * more importantly it exposes us to possible loss of both current and
         * previous checkpoint records if the machine crashes just as we're
         * writing the update. (Perhaps it'd make even more sense to
         * checkpoint only when the previous checkpoint record is in a
         * different xlog page?)
         *
         * We have to make two tests to determine that nothing has happened since
         * the start of the last checkpoint: current insertion point must
         * match the end of the last checkpoint record, and its redo pointer
         * must point to itself.
         */
        if (!shutdown && !force)
        {
                XLogRecPtr      curInsert;

                INSERT_RECPTR(curInsert, Insert, Insert->curridx);
                if (curInsert.xlogid == ControlFile->checkPoint.xlogid &&
                        curInsert.xrecoff == ControlFile->checkPoint.xrecoff +
                        MAXALIGN(SizeOfXLogRecord + sizeof(CheckPoint)) &&
                        ControlFile->checkPoint.xlogid ==
                        ControlFile->checkPointCopy.redo.xlogid &&
                        ControlFile->checkPoint.xrecoff ==
                        ControlFile->checkPointCopy.redo.xrecoff)
                {
                        LWLockRelease(WALInsertLock);
                        LWLockRelease(CheckpointStartLock);
                        LWLockRelease(CheckpointLock);
                        END_CRIT_SECTION();
                        return;
                }
        }

        /*
         * Compute new REDO record ptr = location of next XLOG record.
         *
         * NB: this is NOT necessarily where the checkpoint record itself will
         * be, since other backends may insert more XLOG records while we're
         * off doing the buffer flush work.  Those XLOG records are logically
         * after the checkpoint, even though physically before it.      Got that?
         */
        freespace = INSERT_FREESPACE(Insert);
        if (freespace < SizeOfXLogRecord)
        {
                (void) AdvanceXLInsertBuffer();
                /* OK to ignore update return flag, since we will do flush anyway */
                freespace = INSERT_FREESPACE(Insert);
        }
        INSERT_RECPTR(checkPoint.redo, Insert, Insert->curridx);

        /*
         * Here we update the shared RedoRecPtr for future XLogInsert calls;
         * this must be done while holding the insert lock AND the info_lck.
         *
         * Note: if we fail to complete the checkpoint, RedoRecPtr will be left
         * pointing past where it really needs to point.  This is okay; the
         * only consequence is that XLogInsert might back up whole buffers
         * that it didn't really need to.  We can't postpone advancing
         * RedoRecPtr because XLogInserts that happen while we are dumping
         * buffers must assume that their buffer changes are not included in
         * the checkpoint.
         */
        {
                /* use volatile pointer to prevent code rearrangement */
                volatile XLogCtlData *xlogctl = XLogCtl;

                SpinLockAcquire_NoHoldoff(&xlogctl->info_lck);
                RedoRecPtr = xlogctl->Insert.RedoRecPtr = checkPoint.redo;
                SpinLockRelease_NoHoldoff(&xlogctl->info_lck);
        }

        /*
         * Get UNDO record ptr - this is oldest of PGPROC->logRec values. We
         * do this while holding insert lock to ensure that we won't miss any
         * about-to-commit transactions (UNDO must include all xacts that have
         * commits after REDO point).
         *
         * XXX temporarily ifdef'd out to avoid three-way deadlock condition:
         * GetUndoRecPtr needs to grab SInvalLock to ensure that it is looking
         * at a stable set of proc records, but grabbing SInvalLock while
         * holding WALInsertLock is no good.  GetNewTransactionId may cause a
         * WAL record to be written while holding XidGenLock, and
         * GetSnapshotData needs to get XidGenLock while holding SInvalLock,
         * so there's a risk of deadlock. Need to find a better solution.  See
         * pgsql-hackers discussion of 17-Dec-01.
         *
         * XXX actually, the whole UNDO code is dead code and unlikely to ever be
         * revived, so the lack of a good solution here is not troubling.
         */
#ifdef NOT_USED
        checkPoint.undo = GetUndoRecPtr();

        if (shutdown && checkPoint.undo.xrecoff != 0)
                elog(PANIC, "active transaction while database system is shutting down");
#endif

        /*
         * Now we can release insert lock and checkpoint start lock, allowing
         * other xacts to proceed even while we are flushing disk buffers.
         */
        LWLockRelease(WALInsertLock);

        LWLockRelease(CheckpointStartLock);

        /*
         * Get the other info we need for the checkpoint record.
         */
        LWLockAcquire(XidGenLock, LW_SHARED);
        checkPoint.nextXid = ShmemVariableCache->nextXid;
        LWLockRelease(XidGenLock);

        LWLockAcquire(OidGenLock, LW_SHARED);
        checkPoint.nextOid = ShmemVariableCache->nextOid;
        if (!shutdown)
                checkPoint.nextOid += ShmemVariableCache->oidCount;
        LWLockRelease(OidGenLock);

        /*
         * Having constructed the checkpoint record, ensure all shmem disk
         * buffers and commit-log buffers are flushed to disk.
         *
         * This I/O could fail for various reasons.  If so, we will fail to
         * complete the checkpoint, but there is no reason to force a system
         * panic.  Accordingly, exit critical section while doing it.
         */
        END_CRIT_SECTION();

        CheckPointCLOG();
        CheckPointSUBTRANS();
        FlushBufferPool();

        START_CRIT_SECTION();

        /*
         * Now insert the checkpoint record into XLOG.
         */
        rdata.buffer = InvalidBuffer;
        rdata.data = (char *) (&checkPoint);
        rdata.len = sizeof(checkPoint);
        rdata.next = NULL;

        recptr = XLogInsert(RM_XLOG_ID,
                                                shutdown ? XLOG_CHECKPOINT_SHUTDOWN :
                                                XLOG_CHECKPOINT_ONLINE,
                                                &rdata);

        XLogFlush(recptr);

        /*
         * We now have ProcLastRecPtr = start of actual checkpoint record,
         * recptr = end of actual checkpoint record.
         */
        if (shutdown && !XLByteEQ(checkPoint.redo, ProcLastRecPtr))
                ereport(PANIC,
                                (errmsg("concurrent transaction log activity while database system is shutting down")));

        /*
         * Select point at which we can truncate the log, which we base on the
         * prior checkpoint's earliest info.
         *
         * With UNDO support: oldest item is redo or undo, whichever is older;
         * but watch out for case that undo = 0.
         *
         * Without UNDO support: just use the redo pointer.  This allows xlog
         * space to be freed much faster when there are long-running
         * transactions.
         */
#ifdef NOT_USED
        if (ControlFile->checkPointCopy.undo.xrecoff != 0 &&
                XLByteLT(ControlFile->checkPointCopy.undo,
                                 ControlFile->checkPointCopy.redo))
                XLByteToSeg(ControlFile->checkPointCopy.undo, _logId, _logSeg);
        else
#endif
                XLByteToSeg(ControlFile->checkPointCopy.redo, _logId, _logSeg);

        /*
         * Update the control file.
         */
        LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
        if (shutdown)
                ControlFile->state = DB_SHUTDOWNED;
        ControlFile->prevCheckPoint = ControlFile->checkPoint;
        ControlFile->checkPoint = ProcLastRecPtr;
        ControlFile->checkPointCopy = checkPoint;
        ControlFile->time = time(NULL);
        UpdateControlFile();
        LWLockRelease(ControlFileLock);

        /*
         * We are now done with critical updates; no need for system panic if
         * we have trouble while fooling with offline log segments.
         */
        END_CRIT_SECTION();

        /*
         * Delete offline log files (those no longer needed even for previous
         * checkpoint).
         */
        if (_logId || _logSeg)
        {
                PrevLogSeg(_logId, _logSeg);
                MoveOfflineLogs(_logId, _logSeg, recptr);
        }

        /*
         * Make more log segments if needed.  (Do this after deleting offline
         * log segments, to avoid having peak disk space usage higher than
         * necessary.)
         */
        if (!shutdown)
                PreallocXlogFiles(recptr);

        /*
         * Truncate pg_subtrans if possible.  We can throw away all data
         * before the oldest XMIN of any running transaction.  No future
         * transaction will attempt to reference any pg_subtrans entry older
         * than that (see Asserts in subtrans.c).  During recovery, though, we
         * mustn't do this because StartupSUBTRANS hasn't been called yet.
         */
        if (!InRecovery)
                TruncateSUBTRANS(GetOldestXmin(true));

        LWLockRelease(CheckpointLock);
}

/*
 * Write a NEXTOID log record
 */
void
XLogPutNextOid(Oid nextOid)
{
        XLogRecData rdata;

        rdata.buffer = InvalidBuffer;
        rdata.data = (char *) (&nextOid);
        rdata.len = sizeof(Oid);
        rdata.next = NULL;
        (void) XLogInsert(RM_XLOG_ID, XLOG_NEXTOID, &rdata);
}

/*
 * XLOG resource manager's routines
 */
void
xlog_redo(XLogRecPtr lsn, XLogRecord *record)
{
        uint8           info = record->xl_info & ~XLR_INFO_MASK;

        if (info == XLOG_NEXTOID)
        {
                Oid                     nextOid;

                memcpy(&nextOid, XLogRecGetData(record), sizeof(Oid));
                if (ShmemVariableCache->nextOid < nextOid)
                {
                        ShmemVariableCache->nextOid = nextOid;
                        ShmemVariableCache->oidCount = 0;
                }
        }
        else if (info == XLOG_CHECKPOINT_SHUTDOWN)
        {
                CheckPoint      checkPoint;

                memcpy(&checkPoint, XLogRecGetData(record), sizeof(CheckPoint));
                /* In a SHUTDOWN checkpoint, believe the counters exactly */
                ShmemVariableCache->nextXid = checkPoint.nextXid;
                ShmemVariableCache->nextOid = checkPoint.nextOid;
                ShmemVariableCache->oidCount = 0;

                /*
                 * TLI may change in a shutdown checkpoint, but it shouldn't
                 * decrease
                 */
                if (checkPoint.ThisTimeLineID != ThisTimeLineID)
                {
                        if (checkPoint.ThisTimeLineID < ThisTimeLineID ||
                                !list_member_int(expectedTLIs,
                                                                 (int) checkPoint.ThisTimeLineID))
                                ereport(PANIC,
                                                (errmsg("unexpected timeline ID %u (after %u) in checkpoint record",
                                                        checkPoint.ThisTimeLineID, ThisTimeLineID)));
                        /* Following WAL records should be run with new TLI */
                        ThisTimeLineID = checkPoint.ThisTimeLineID;
                }
        }
        else if (info == XLOG_CHECKPOINT_ONLINE)
        {
                CheckPoint      checkPoint;

                memcpy(&checkPoint, XLogRecGetData(record), sizeof(CheckPoint));
                /* In an ONLINE checkpoint, treat the counters like NEXTOID */
                if (TransactionIdPrecedes(ShmemVariableCache->nextXid,
                                                                  checkPoint.nextXid))
                        ShmemVariableCache->nextXid = checkPoint.nextXid;
                if (ShmemVariableCache->nextOid < checkPoint.nextOid)
                {
                        ShmemVariableCache->nextOid = checkPoint.nextOid;
                        ShmemVariableCache->oidCount = 0;
                }
                /* TLI should not change in an on-line checkpoint */
                if (checkPoint.ThisTimeLineID != ThisTimeLineID)
                        ereport(PANIC,
                                        (errmsg("unexpected timeline ID %u (should be %u) in checkpoint record",
                                                        checkPoint.ThisTimeLineID, ThisTimeLineID)));
        }
}

void
xlog_undo(XLogRecPtr lsn, XLogRecord *record)
{
}

void
xlog_desc(char *buf, uint8 xl_info, char *rec)
{
        uint8           info = xl_info & ~XLR_INFO_MASK;

        if (info == XLOG_CHECKPOINT_SHUTDOWN ||
                info == XLOG_CHECKPOINT_ONLINE)
        {
                CheckPoint *checkpoint = (CheckPoint *) rec;

                sprintf(buf + strlen(buf), "checkpoint: redo %X/%X; undo %X/%X; "
                                "tli %u; xid %u; oid %u; %s",
                                checkpoint->redo.xlogid, checkpoint->redo.xrecoff,
                                checkpoint->undo.xlogid, checkpoint->undo.xrecoff,
                                checkpoint->ThisTimeLineID, checkpoint->nextXid,
                                checkpoint->nextOid,
                         (info == XLOG_CHECKPOINT_SHUTDOWN) ? "shutdown" : "online");
        }
        else if (info == XLOG_NEXTOID)
        {
                Oid                     nextOid;

                memcpy(&nextOid, rec, sizeof(Oid));
                sprintf(buf + strlen(buf), "nextOid: %u", nextOid);
        }
        else
                strcat(buf, "UNKNOWN");
}

#ifdef WAL_DEBUG

static void
xlog_outrec(char *buf, XLogRecord *record)
{
        int                     bkpb;
        int                     i;

        sprintf(buf + strlen(buf), "prev %X/%X; xid %u",
                        record->xl_prev.xlogid, record->xl_prev.xrecoff,
                        record->xl_xid);

        for (i = 0, bkpb = 0; i < XLR_MAX_BKP_BLOCKS; i++)
        {
                if (!(record->xl_info & (XLR_SET_BKP_BLOCK(i))))
                        continue;
                bkpb++;
        }

        if (bkpb)
                sprintf(buf + strlen(buf), "; bkpb %d", bkpb);

        sprintf(buf + strlen(buf), ": %s",
                        RmgrTable[record->xl_rmid].rm_name);
}
#endif   /* WAL_DEBUG */


/*
 * GUC support
 */
const char *
assign_xlog_sync_method(const char *method, bool doit, GucSource source)
{
        int                     new_sync_method;
        int                     new_sync_bit;

        if (pg_strcasecmp(method, "fsync") == 0)
        {
                new_sync_method = SYNC_METHOD_FSYNC;
                new_sync_bit = 0;
        }
#ifdef HAVE_FDATASYNC
        else if (pg_strcasecmp(method, "fdatasync") == 0)
        {
                new_sync_method = SYNC_METHOD_FDATASYNC;
                new_sync_bit = 0;
        }
#endif
#ifdef OPEN_SYNC_FLAG
        else if (pg_strcasecmp(method, "open_sync") == 0)
        {
                new_sync_method = SYNC_METHOD_OPEN;
                new_sync_bit = OPEN_SYNC_FLAG;
        }
#endif
#ifdef OPEN_DATASYNC_FLAG
        else if (pg_strcasecmp(method, "open_datasync") == 0)
        {
                new_sync_method = SYNC_METHOD_OPEN;
                new_sync_bit = OPEN_DATASYNC_FLAG;
        }
#endif
        else
                return NULL;

        if (!doit)
                return method;

        if (sync_method != new_sync_method || open_sync_bit != new_sync_bit)
        {
                /*
                 * To ensure that no blocks escape unsynced, force an fsync on the
                 * currently open log segment (if any).  Also, if the open flag is
                 * changing, close the log file so it will be reopened (with new
                 * flag bit) at next use.
                 */
                if (openLogFile >= 0)
                {
                        if (pg_fsync(openLogFile) != 0)
                                ereport(PANIC,
                                                (errcode_for_file_access(),
                                        errmsg("could not fsync log file %u, segment %u: %m",
                                                   openLogId, openLogSeg)));
                        if (open_sync_bit != new_sync_bit)
                        {
                                if (close(openLogFile))
                                        ereport(PANIC,
                                                        (errcode_for_file_access(),
                                        errmsg("could not close log file %u, segment %u: %m",
                                                   openLogId, openLogSeg)));
                                openLogFile = -1;
                        }
                }
                sync_method = new_sync_method;
                open_sync_bit = new_sync_bit;
        }

        return method;
}


/*
 * Issue appropriate kind of fsync (if any) on the current XLOG output file
 */
static void
issue_xlog_fsync(void)
{
        switch (sync_method)
        {
                case SYNC_METHOD_FSYNC:
                        if (pg_fsync(openLogFile) != 0)
                                ereport(PANIC,
                                                (errcode_for_file_access(),
                                        errmsg("could not fsync log file %u, segment %u: %m",
                                                   openLogId, openLogSeg)));
                        break;
#ifdef HAVE_FDATASYNC
                case SYNC_METHOD_FDATASYNC:
                        if (pg_fdatasync(openLogFile) != 0)
                                ereport(PANIC,
                                                (errcode_for_file_access(),
                                errmsg("could not fdatasync log file %u, segment %u: %m",
                                           openLogId, openLogSeg)));
                        break;
#endif
                case SYNC_METHOD_OPEN:
                        /* write synced it already */
                        break;
                default:
                        elog(PANIC, "unrecognized wal_sync_method: %d", sync_method);
                        break;
        }
}


/*
 * pg_start_backup: set up for taking an on-line backup dump
 *
 * Essentially what this does is to create a backup label file in $PGDATA,
 * where it will be archived as part of the backup dump.  The label file
 * contains the user-supplied label string (typically this would be used
 * to tell where the backup dump will be stored) and the starting time and
 * starting WAL offset for the dump.
 */
Datum
pg_start_backup(PG_FUNCTION_ARGS)
{
        text       *backupid = PG_GETARG_TEXT_P(0);
        text       *result;
        char       *backupidstr;
        XLogRecPtr      checkpointloc;
        XLogRecPtr      startpoint;
        time_t          stamp_time;
        char            strfbuf[128];
        char            labelfilepath[MAXPGPATH];
        char            xlogfilename[MAXFNAMELEN];
        uint32          _logId;
        uint32          _logSeg;
        struct stat stat_buf;
        FILE       *fp;

        if (!superuser())
                ereport(ERROR,
                                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                                 (errmsg("must be superuser to run a backup"))));
        backupidstr = DatumGetCString(DirectFunctionCall1(textout,
                                                                                         PointerGetDatum(backupid)));

        /*
         * Force a CHECKPOINT.  This is not strictly necessary, but it seems
         * like a good idea to minimize the amount of past WAL needed to use
         * the backup.  Also, this guarantees that two successive backup runs
         * will have different checkpoint positions and hence different
         * history file names, even if nothing happened in between.
         */
        RequestCheckpoint(true);

        /*
         * Now we need to fetch the checkpoint record location, and also its
         * REDO pointer.  The oldest point in WAL that would be needed to
         * restore starting from the checkpoint is precisely the REDO pointer.
         */
        LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
        checkpointloc = ControlFile->checkPoint;
        startpoint = ControlFile->checkPointCopy.redo;
        LWLockRelease(ControlFileLock);

        XLByteToSeg(startpoint, _logId, _logSeg);
        XLogFileName(xlogfilename, ThisTimeLineID, _logId, _logSeg);

        /*
         * We deliberately use strftime/localtime not the src/timezone
         * functions, so that backup labels will consistently be recorded in
         * the same timezone regardless of TimeZone setting.  This matches
         * elog.c's practice.
         */
        stamp_time = time(NULL);
        strftime(strfbuf, sizeof(strfbuf),
                         "%Y-%m-%d %H:%M:%S %Z",
                         localtime(&stamp_time));

        /*
         * Check for existing backup label --- implies a backup is already
         * running
         */
        snprintf(labelfilepath, MAXPGPATH, "%s/backup_label", DataDir);
        if (stat(labelfilepath, &stat_buf) != 0)
        {
                if (errno != ENOENT)
                        ereport(ERROR,
                                        (errcode_for_file_access(),
                                         errmsg("could not stat \"%s\": %m",
                                                        labelfilepath)));
        }
        else
                ereport(ERROR,
                                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                                 errmsg("a backup is already in progress"),
                                 errhint("If you're sure there is no backup in progress, remove file \"%s\" and try again.",
                                                 labelfilepath)));

        /*
         * Okay, write the file
         */
        fp = AllocateFile(labelfilepath, "w");
        if (!fp)
                ereport(ERROR,
                                (errcode_for_file_access(),
                                 errmsg("could not create file \"%s\": %m",
                                                labelfilepath)));
        fprintf(fp, "START WAL LOCATION: %X/%X (file %s)\n",
                        startpoint.xlogid, startpoint.xrecoff, xlogfilename);
        fprintf(fp, "CHECKPOINT LOCATION: %X/%X\n",
                        checkpointloc.xlogid, checkpointloc.xrecoff);
        fprintf(fp, "START TIME: %s\n", strfbuf);
        fprintf(fp, "LABEL: %s\n", backupidstr);
        if (fflush(fp) || ferror(fp) || FreeFile(fp))
                ereport(ERROR,
                                (errcode_for_file_access(),
                                 errmsg("could not write file \"%s\": %m",
                                                labelfilepath)));

        /*
         * We're done.  As a convenience, return the starting WAL offset.
         */
        snprintf(xlogfilename, sizeof(xlogfilename), "%X/%X",
                         startpoint.xlogid, startpoint.xrecoff);
        result = DatumGetTextP(DirectFunctionCall1(textin,
                                                                                 CStringGetDatum(xlogfilename)));
        PG_RETURN_TEXT_P(result);
}

/*
 * pg_stop_backup: finish taking an on-line backup dump
 *
 * We remove the backup label file created by pg_start_backup, and instead
 * create a backup history file in pg_xlog (whence it will immediately be
 * archived).  The backup history file contains the same info found in
 * the label file, plus the backup-end time and WAL offset.
 */
Datum
pg_stop_backup(PG_FUNCTION_ARGS)
{
        text       *result;
        XLogCtlInsert *Insert = &XLogCtl->Insert;
        XLogRecPtr      startpoint;
        XLogRecPtr      stoppoint;
        time_t          stamp_time;
        char            strfbuf[128];
        char            labelfilepath[MAXPGPATH];
        char            histfilepath[MAXPGPATH];
        char            startxlogfilename[MAXFNAMELEN];
        char            stopxlogfilename[MAXFNAMELEN];
        uint32          _logId;
        uint32          _logSeg;
        FILE       *lfp;
        FILE       *fp;
        char            ch;
        int                     ich;

        if (!superuser())
                ereport(ERROR,
                                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                                 (errmsg("must be superuser to run a backup"))));

        /*
         * Get the current end-of-WAL position; it will be unsafe to use this
         * dump to restore to a point in advance of this time.
         */
        LWLockAcquire(WALInsertLock, LW_EXCLUSIVE);
        INSERT_RECPTR(stoppoint, Insert, Insert->curridx);
        LWLockRelease(WALInsertLock);

        XLByteToSeg(stoppoint, _logId, _logSeg);
        XLogFileName(stopxlogfilename, ThisTimeLineID, _logId, _logSeg);

        /*
         * We deliberately use strftime/localtime not the src/timezone
         * functions, so that backup labels will consistently be recorded in
         * the same timezone regardless of TimeZone setting.  This matches
         * elog.c's practice.
         */
        stamp_time = time(NULL);
        strftime(strfbuf, sizeof(strfbuf),
                         "%Y-%m-%d %H:%M:%S %Z",
                         localtime(&stamp_time));

        /*
         * Open the existing label file
         */
        snprintf(labelfilepath, MAXPGPATH, "%s/backup_label", DataDir);
        lfp = AllocateFile(labelfilepath, "r");
        if (!lfp)
        {
                if (errno != ENOENT)
                        ereport(ERROR,
                                        (errcode_for_file_access(),
                                         errmsg("could not read file \"%s\": %m",
                                                        labelfilepath)));
                ereport(ERROR,
                                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                                 errmsg("a backup is not in progress")));
        }

        /*
         * Read and parse the START WAL LOCATION line (this code is pretty
         * crude, but we are not expecting any variability in the file
         * format).
         */
        if (fscanf(lfp, "START WAL LOCATION: %X/%X (file %24s)%c",
                           &startpoint.xlogid, &startpoint.xrecoff, startxlogfilename,
                           &ch) != 4 || ch != '\n')
                ereport(ERROR,
                                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                                 errmsg("invalid data in file \"%s\"", labelfilepath)));

        /*
         * Write the backup history file
         */
        XLByteToSeg(startpoint, _logId, _logSeg);
        BackupHistoryFilePath(histfilepath, ThisTimeLineID, _logId, _logSeg,
                                                  startpoint.xrecoff % XLogSegSize);
        fp = AllocateFile(histfilepath, "w");
        if (!fp)
                ereport(ERROR,
                                (errcode_for_file_access(),
                                 errmsg("could not create file \"%s\": %m",
                                                histfilepath)));
        fprintf(fp, "START WAL LOCATION: %X/%X (file %s)\n",
                        startpoint.xlogid, startpoint.xrecoff, startxlogfilename);
        fprintf(fp, "STOP WAL LOCATION: %X/%X (file %s)\n",
                        stoppoint.xlogid, stoppoint.xrecoff, stopxlogfilename);
        /* transfer remaining lines from label to history file */
        while ((ich = fgetc(lfp)) != EOF)
                fputc(ich, fp);
        fprintf(fp, "STOP TIME: %s\n", strfbuf);
        if (fflush(fp) || ferror(fp) || FreeFile(fp))
                ereport(ERROR,
                                (errcode_for_file_access(),
                                 errmsg("could not write file \"%s\": %m",
                                                histfilepath)));

        /*
         * Close and remove the backup label file
         */
        if (ferror(lfp) || FreeFile(lfp))
                ereport(ERROR,
                                (errcode_for_file_access(),
                                 errmsg("could not read file \"%s\": %m",
                                                labelfilepath)));
        if (unlink(labelfilepath) != 0)
                ereport(ERROR,
                                (errcode_for_file_access(),
                                 errmsg("could not remove file \"%s\": %m",
                                                labelfilepath)));

        /*
         * Notify archiver that history file may be archived immediately
         */
        if (XLogArchivingActive())
        {
                BackupHistoryFileName(histfilepath, ThisTimeLineID, _logId, _logSeg,
                                                          startpoint.xrecoff % XLogSegSize);
                XLogArchiveNotify(histfilepath);
        }

        /*
         * We're done.  As a convenience, return the ending WAL offset.
         */
        snprintf(stopxlogfilename, sizeof(stopxlogfilename), "%X/%X",
                         stoppoint.xlogid, stoppoint.xrecoff);
        result = DatumGetTextP(DirectFunctionCall1(textin,
                                                                         CStringGetDatum(stopxlogfilename)));
        PG_RETURN_TEXT_P(result);
}

/*
 * read_backup_label: check to see if a backup_label file is present
 *
 * If we see a backup_label during recovery, we assume that we are recovering
 * from a backup dump file, and we therefore roll forward from the checkpoint
 * identified by the label file, NOT what pg_control says.      This avoids the
 * problem that pg_control might have been archived one or more checkpoints
 * later than the start of the dump, and so if we rely on it as the start
 * point, we will fail to restore a consistent database state.
 *
 * We also attempt to retrieve the corresponding backup history file.
 * If successful, set recoveryMinXlogOffset to constrain valid PITR stopping
 * points.
 *
 * Returns TRUE if a backup_label was found (and fills the checkpoint
 * location into *checkPointLoc); returns FALSE if not.
 */
static bool
read_backup_label(XLogRecPtr *checkPointLoc)
{
        XLogRecPtr      startpoint;
        XLogRecPtr      stoppoint;
        char            labelfilepath[MAXPGPATH];
        char            histfilename[MAXFNAMELEN];
        char            histfilepath[MAXPGPATH];
        char            startxlogfilename[MAXFNAMELEN];
        char            stopxlogfilename[MAXFNAMELEN];
        TimeLineID      tli;
        uint32          _logId;
        uint32          _logSeg;
        FILE       *lfp;
        FILE       *fp;
        char            ch;

        /*
         * See if label file is present
         */
        snprintf(labelfilepath, MAXPGPATH, "%s/backup_label", DataDir);
        lfp = AllocateFile(labelfilepath, "r");
        if (!lfp)
        {
                if (errno != ENOENT)
                        ereport(FATAL,
                                        (errcode_for_file_access(),
                                         errmsg("could not read file \"%s\": %m",
                                                        labelfilepath)));
                return false;                   /* it's not there, all is fine */
        }

        /*
         * Read and parse the START WAL LOCATION and CHECKPOINT lines (this
         * code is pretty crude, but we are not expecting any variability in
         * the file format).
         */
        if (fscanf(lfp, "START WAL LOCATION: %X/%X (file %08X%16s)%c",
                           &startpoint.xlogid, &startpoint.xrecoff, &tli,
                           startxlogfilename, &ch) != 5 || ch != '\n')
                ereport(FATAL,
                                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                                 errmsg("invalid data in file \"%s\"", labelfilepath)));
        if (fscanf(lfp, "CHECKPOINT LOCATION: %X/%X%c",
                           &checkPointLoc->xlogid, &checkPointLoc->xrecoff,
                           &ch) != 3 || ch != '\n')
                ereport(FATAL,
                                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                                 errmsg("invalid data in file \"%s\"", labelfilepath)));
        if (ferror(lfp) || FreeFile(lfp))
                ereport(FATAL,
                                (errcode_for_file_access(),
                                 errmsg("could not read file \"%s\": %m",
                                                labelfilepath)));

        /*
         * Try to retrieve the backup history file (no error if we can't)
         */
        XLByteToSeg(startpoint, _logId, _logSeg);
        BackupHistoryFileName(histfilename, tli, _logId, _logSeg,
                                                  startpoint.xrecoff % XLogSegSize);

        if (InArchiveRecovery)
                RestoreArchivedFile(histfilepath, histfilename, "RECOVERYHISTORY", 0);
        else
                BackupHistoryFilePath(histfilepath, tli, _logId, _logSeg,
                                                          startpoint.xrecoff % XLogSegSize);

        fp = AllocateFile(histfilepath, "r");
        if (fp)
        {
                /*
                 * Parse history file to identify stop point.
                 */
                if (fscanf(fp, "START WAL LOCATION: %X/%X (file %24s)%c",
                          &startpoint.xlogid, &startpoint.xrecoff, startxlogfilename,
                                   &ch) != 4 || ch != '\n')
                        ereport(FATAL,
                                        (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                                   errmsg("invalid data in file \"%s\"", histfilename)));
                if (fscanf(fp, "STOP WAL LOCATION: %X/%X (file %24s)%c",
                                 &stoppoint.xlogid, &stoppoint.xrecoff, stopxlogfilename,
                                   &ch) != 4 || ch != '\n')
                        ereport(FATAL,
                                        (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                                   errmsg("invalid data in file \"%s\"", histfilename)));
                recoveryMinXlogOffset = stoppoint;
                if (ferror(fp) || FreeFile(fp))
                        ereport(FATAL,
                                        (errcode_for_file_access(),
                                         errmsg("could not read file \"%s\": %m",
                                                        histfilepath)));
        }

        return true;
}

/*
 * remove_backup_label: remove any extant backup_label after successful
 * recovery.  Once we have completed the end-of-recovery checkpoint there
 * is no reason to have to replay from the start point indicated by the
 * label (and indeed we'll probably have removed/recycled the needed WAL
 * segments), so remove the label to prevent trouble in later crash recoveries.
 */
static void
remove_backup_label(void)
{
        char            labelfilepath[MAXPGPATH];

        snprintf(labelfilepath, MAXPGPATH, "%s/backup_label", DataDir);
        if (unlink(labelfilepath) != 0)
                if (errno != ENOENT)
                        ereport(FATAL,
                                        (errcode_for_file_access(),
                                         errmsg("could not remove file \"%s\": %m",
                                                        labelfilepath)));
}