4 * PostgreSQL transaction log manager
6 * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
7 * Portions Copyright (c) 1994, Regents of the University of California
9 * $PostgreSQL: pgsql/src/include/access/xlog.h,v 1.74 2006/08/21 16:16:31 tgl Exp $
14 #include "access/rmgr.h"
15 #include "access/xlogdefs.h"
16 #include "lib/stringinfo.h"
17 #include "storage/buf.h"
18 #include "utils/pg_crc.h"
22 * The overall layout of an XLOG record is:
23 * Fixed-size header (XLogRecord struct)
31 * where there can be zero to three backup blocks (as signaled by xl_info flag
32 * bits). XLogRecord structs always start on MAXALIGN boundaries in the WAL
33 * files, and we round up SizeOfXLogRecord so that the rmgr data is also
34 * guaranteed to begin on a MAXALIGN boundary. However, no padding is added
35 * to align BkpBlock structs or backup block data.
37 * NOTE: xl_len counts only the rmgr data, not the XLogRecord header,
38 * and also not any backup blocks. xl_tot_len counts everything. Neither
39 * length field is rounded up to an alignment boundary.
41 typedef struct XLogRecord
43 pg_crc32 xl_crc; /* CRC for this record */
44 XLogRecPtr xl_prev; /* ptr to previous record in log */
45 TransactionId xl_xid; /* xact id */
46 uint32 xl_tot_len; /* total len of entire record */
47 uint32 xl_len; /* total len of rmgr data */
48 uint8 xl_info; /* flag bits, see below */
49 RmgrId xl_rmid; /* resource manager for this record */
51 /* Depending on MAXALIGN, there are either 2 or 6 wasted bytes here */
53 /* ACTUAL LOG DATA FOLLOWS AT END OF STRUCT */
57 #define SizeOfXLogRecord MAXALIGN(sizeof(XLogRecord))
59 #define XLogRecGetData(record) ((char*) (record) + SizeOfXLogRecord)
62 * XLOG uses only low 4 bits of xl_info. High 4 bits may be used by rmgr.
64 #define XLR_INFO_MASK 0x0F
67 * If we backed up any disk blocks with the XLOG record, we use flag bits in
68 * xl_info to signal it. We support backup of up to 3 disk blocks per XLOG
69 * record. (Could support 4 if we cared to dedicate all the xl_info bits for
70 * this purpose; currently bit 0 of xl_info is unused and available.)
72 #define XLR_BKP_BLOCK_MASK 0x0E /* all info bits used for bkp blocks */
73 #define XLR_MAX_BKP_BLOCKS 3
74 #define XLR_SET_BKP_BLOCK(iblk) (0x08 >> (iblk))
75 #define XLR_BKP_BLOCK_1 XLR_SET_BKP_BLOCK(0) /* 0x08 */
76 #define XLR_BKP_BLOCK_2 XLR_SET_BKP_BLOCK(1) /* 0x04 */
77 #define XLR_BKP_BLOCK_3 XLR_SET_BKP_BLOCK(2) /* 0x02 */
80 * Sometimes we log records which are out of transaction control.
81 * Rmgr may "or" XLOG_NO_TRAN into info passed to XLogInsert to indicate this.
83 #define XLOG_NO_TRAN XLR_INFO_MASK
86 #define SYNC_METHOD_FSYNC 0
87 #define SYNC_METHOD_FDATASYNC 1
88 #define SYNC_METHOD_OPEN 2 /* for O_SYNC and O_DSYNC */
89 #define SYNC_METHOD_FSYNC_WRITETHROUGH 3
90 extern int sync_method;
93 * The rmgr data to be written by XLogInsert() is defined by a chain of
94 * one or more XLogRecData structs. (Multiple structs would be used when
95 * parts of the source data aren't physically adjacent in memory, or when
96 * multiple associated buffers need to be specified.)
98 * If buffer is valid then XLOG will check if buffer must be backed up
99 * (ie, whether this is first change of that page since last checkpoint).
100 * If so, the whole page contents are attached to the XLOG record, and XLOG
101 * sets XLR_BKP_BLOCK_X bit in xl_info. Note that the buffer must be pinned
102 * and exclusive-locked by the caller, so that it won't change under us.
103 * NB: when the buffer is backed up, we DO NOT insert the data pointed to by
104 * this XLogRecData struct into the XLOG record, since we assume it's present
105 * in the buffer. Therefore, rmgr redo routines MUST pay attention to
106 * XLR_BKP_BLOCK_X to know what is actually stored in the XLOG record.
107 * The i'th XLR_BKP_BLOCK bit corresponds to the i'th distinct buffer
108 * value (ignoring InvalidBuffer) appearing in the rdata chain.
110 * When buffer is valid, caller must set buffer_std to indicate whether the
111 * page uses standard pd_lower/pd_upper header fields. If this is true, then
112 * XLOG is allowed to omit the free space between pd_lower and pd_upper from
113 * the backed-up page image. Note that even when buffer_std is false, the
114 * page MUST have an LSN field as its first eight bytes!
116 * Note: data can be NULL to indicate no rmgr data associated with this chain
117 * entry. This can be sensible (ie, not a wasted entry) if buffer is valid.
118 * The implication is that the buffer has been changed by the operation being
119 * logged, and so may need to be backed up, but the change can be redone using
120 * only information already present elsewhere in the XLOG entry.
122 typedef struct XLogRecData
124 char *data; /* start of rmgr data to include */
125 uint32 len; /* length of rmgr data to include */
126 Buffer buffer; /* buffer associated with data, if any */
127 bool buffer_std; /* buffer has standard pd_lower/pd_upper */
128 struct XLogRecData *next; /* next struct in chain, or NULL */
131 extern TimeLineID ThisTimeLineID; /* current TLI */
132 extern bool InRecovery;
133 extern XLogRecPtr MyLastRecPtr;
134 extern bool MyXactMadeXLogEntry;
135 extern bool MyXactMadeTempRelUpdate;
136 extern XLogRecPtr ProcLastRecEnd;
138 /* these variables are GUC parameters related to XLOG */
139 extern int CheckPointSegments;
140 extern int XLOGbuffers;
141 extern char *XLogArchiveCommand;
142 extern int XLogArchiveTimeout;
143 extern char *XLOG_sync_method;
144 extern const char XLOG_sync_method_default[];
146 #define XLogArchivingActive() (XLogArchiveCommand[0] != '\0')
149 extern bool XLOG_DEBUG;
152 extern XLogRecPtr XLogInsert(RmgrId rmid, uint8 info, XLogRecData *rdata);
153 extern void XLogFlush(XLogRecPtr RecPtr);
155 extern void xlog_redo(XLogRecPtr lsn, XLogRecord *record);
156 extern void xlog_desc(StringInfo buf, uint8 xl_info, char *rec);
158 extern void UpdateControlFile(void);
159 extern Size XLOGShmemSize(void);
160 extern void XLOGShmemInit(void);
161 extern void BootStrapXLOG(void);
162 extern void StartupXLOG(void);
163 extern void ShutdownXLOG(int code, Datum arg);
164 extern void InitXLOGAccess(void);
165 extern void CreateCheckPoint(bool shutdown, bool force);
166 extern void XLogPutNextOid(Oid nextOid);
167 extern XLogRecPtr GetRedoRecPtr(void);
168 extern TransactionId GetRecentNextXid(void);
169 extern void GetNextXidAndEpoch(TransactionId *xid, uint32 *epoch);