-<!-- $Header: /cvsroot/pgsql/doc/src/sgml/wal.sgml,v 1.2 2001/02/18 04:50:43 tgl Exp $ -->
+<!-- $Header: /cvsroot/pgsql/doc/src/sgml/wal.sgml,v 1.3 2001/02/26 00:50:07 tgl Exp $ -->
<chapter id="wal">
<title>Write-Ahead Logging (<acronym>WAL</acronym>)</title>
record to the log with <function>LogInsert</function> but before
performing a <function>LogFlush</function>. This delay allows other
backends to add their commit records to the log so as to have all
- of them flushed with a single log sync. Unfortunately, this
- mechanism is not fully implemented at release 7.1, so there is at
- present usually no benefit to be gained from increasing this parameter
- above its default value of zero.
+ of them flushed with a single log sync. No sleep will occur if fsync
+ is not enabled or if fewer than <varname>COMMIT_SIBLINGS</varname>
+ other backends are not currently in active transactions; this avoids
+ sleeping when it's unlikely that any other backend will commit soon.
+ Note that on most platforms, the resolution of a sleep request is
+ ten milliseconds, so that any nonzero <varname>COMMIT_DELAY</varname>
+ setting between 1 and 10000 microseconds will have the same effect.
</para>
</sect1>
</chapter>
*
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/access/transam/xact.c,v 1.97 2001/02/18 04:50:43 tgl Exp $
+ * $Header: /cvsroot/pgsql/src/backend/access/transam/xact.c,v 1.98 2001/02/26 00:50:07 tgl Exp $
*
* NOTES
* Transaction aborts can now occur two ways:
#include <sys/time.h>
#include "access/nbtree.h"
+#include "access/xact.h"
#include "catalog/heap.h"
#include "catalog/index.h"
#include "commands/async.h"
extern bool SharedBufferChanged;
-void RecordTransactionCommit(void);
-
static void AbortTransaction(void);
static void AtAbort_Cache(void);
static void AtAbort_Locks(void);
TransactionState CurrentTransactionState = &CurrentTransactionStateData;
+/*
+ * User-tweakable parameters
+ */
int DefaultXactIsoLevel = XACT_READ_COMMITTED;
int XactIsoLevel;
-#include "access/xlogutils.h"
-
-int CommitDelay = 0; /* in microseconds */
+int CommitDelay = 0; /* precommit delay in microseconds */
+int CommitSiblings = 5; /* number of concurrent xacts needed to sleep */
static void (*_RollbackFunc)(void*) = NULL;
static void *_RollbackData = NULL;
* Sleep before commit! So we can flush more than one
* commit records per single fsync. (The idea is some other
* backend may do the XLogFlush while we're sleeping. This
- * needs work however, because on most Unixen, the minimum
+ * needs work still, because on most Unixen, the minimum
* select() delay is 10msec or more, which is way too long.)
+ *
+ * We do not sleep if enableFsync is not turned on, nor if there
+ * are fewer than CommitSiblings other backends with active
+ * transactions.
*/
- if (CommitDelay > 0)
+ if (CommitDelay > 0 && enableFsync &&
+ CountActiveBackends() >= CommitSiblings)
{
struct timeval delay;
* Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
- * $Header: /cvsroot/pgsql/src/backend/access/transam/xlog.c,v 1.54 2001/02/18 04:39:42 tgl Exp $
+ * $Header: /cvsroot/pgsql/src/backend/access/transam/xlog.c,v 1.55 2001/02/26 00:50:07 tgl Exp $
*
*-------------------------------------------------------------------------
*/
elog(LOG, "database system is shut down");
}
-extern XLogRecPtr GetUndoRecPtr(void);
-
void
CreateCheckPoint(bool shutdown)
{
*
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/storage/ipc/sinval.c,v 1.25 2001/01/24 19:43:07 momjian Exp $
+ * $Header: /cvsroot/pgsql/src/backend/storage/ipc/sinval.c,v 1.26 2001/02/26 00:50:07 tgl Exp $
*
*-------------------------------------------------------------------------
*/
-/* #define INVALIDDEBUG 1 */
+#include "postgres.h"
#include <sys/types.h>
-#include "postgres.h"
-
#include "storage/backendid.h"
#include "storage/proc.h"
#include "storage/sinval.h"
}
/*
- * GetUndoRecPtr -- returns oldest PROC->logRec.
+ * CountActiveBackends --- count backends (other than myself) that are in
+ * active transactions. This is used as a heuristic to decide if
+ * a pre-XLOG-flush delay is worthwhile during commit.
+ *
+ * An active transaction is something that has written at least one XLOG
+ * record; read-only transactions don't count. Also, do not count backends
+ * that are blocked waiting for locks, since they are not going to get to
+ * run until someone else commits.
*/
-XLogRecPtr GetUndoRecPtr(void);
+int
+CountActiveBackends(void)
+{
+ SISeg *segP = shmInvalBuffer;
+ ProcState *stateP = segP->procState;
+ int count = 0;
+ int index;
+ /*
+ * Note: for speed, we don't acquire SInvalLock. This is a little bit
+ * bogus, but since we are only testing xrecoff for zero or nonzero,
+ * it should be OK. The result is only used for heuristic purposes
+ * anyway...
+ */
+ for (index = 0; index < segP->lastBackend; index++)
+ {
+ SHMEM_OFFSET pOffset = stateP[index].procStruct;
+
+ if (pOffset != INVALID_OFFSET)
+ {
+ PROC *proc = (PROC *) MAKE_PTR(pOffset);
+
+ if (proc == MyProc)
+ continue; /* do not count myself */
+ if (proc->logRec.xrecoff == 0)
+ continue; /* do not count if not in a transaction */
+ if (proc->waitLock != NULL)
+ continue; /* do not count if blocked on a lock */
+ count++;
+ }
+ }
+
+ return count;
+}
+
+/*
+ * GetUndoRecPtr -- returns oldest PROC->logRec.
+ */
XLogRecPtr
GetUndoRecPtr(void)
{
* Support for grand unified configuration scheme, including SET
* command, configuration file, and command line options.
*
- * $Header: /cvsroot/pgsql/src/backend/utils/misc/guc.c,v 1.30 2001/02/18 04:50:43 tgl Exp $
+ * $Header: /cvsroot/pgsql/src/backend/utils/misc/guc.c,v 1.31 2001/02/26 00:50:07 tgl Exp $
*
* Copyright 2000 by PostgreSQL Global Development Group
* Written by Peter Eisentraut <peter_e@gmx.net>.
extern int XLOGfiles;
extern int XLOG_DEBUG;
extern int CommitDelay;
+extern int CommitSiblings;
extern bool FixBTree;
{"tcpip_socket", PGC_POSTMASTER, &NetServer, false},
{"ssl", PGC_POSTMASTER, &EnableSSL, false},
- {"fsync", PGC_USERSET, &enableFsync, true},
+ {"fsync", PGC_SIGHUP, &enableFsync, true},
{"silent_mode", PGC_POSTMASTER, &SilentMode, false},
{"log_connections", PGC_SIGHUP, &Log_connections, false},
0777, 0000, 0777},
{"checkpoint_timeout", PGC_POSTMASTER, &CheckPointTimeout,
- 300, 30, 1800},
+ 300, 30, 3600},
{"wal_buffers", PGC_POSTMASTER, &XLOGbuffers,
8, 4, INT_MAX},
{"commit_delay", PGC_USERSET, &CommitDelay,
0, 0, 100000},
+ {"commit_siblings", PGC_USERSET, &CommitSiblings,
+ 5, 1, 1000},
+
{NULL, 0, NULL, 0, 0, 0}
};
#wal_files = 0 # range 0-64
#wal_debug = 0 # range 0-16
#commit_delay = 0 # range 0-100000
-#checkpoint_timeout = 300 # range 30-1800
+#commit_siblings = 5 # range 1-1000
+#checkpoint_timeout = 300 # in seconds, range 30-3600
#
*
* Copyright 2000 by PostgreSQL Global Development Group
*
- * $Header: /cvsroot/pgsql/src/bin/psql/tab-complete.c,v 1.26 2001/02/10 02:31:28 tgl Exp $
+ * $Header: /cvsroot/pgsql/src/bin/psql/tab-complete.c,v 1.27 2001/02/26 00:50:07 tgl Exp $
*/
/*----------------------------------------------------------------------
"debug_level",
"max_expr_depth",
"commit_delay",
+ "commit_siblings",
"effective_cache_size",
"random_page_cost",
*
* PostgreSQL transaction log manager
*
- * $Header: /cvsroot/pgsql/src/include/access/xlog.h,v 1.17 2001/01/14 05:08:16 tgl Exp $
+ * $Header: /cvsroot/pgsql/src/include/access/xlog.h,v 1.18 2001/02/26 00:50:07 tgl Exp $
*/
#ifndef XLOG_H
#define XLOG_H
extern void CreateCheckPoint(bool shutdown);
extern void SetThisStartUpID(void);
+/* in storage/ipc/sinval.c, but don't want to declare in sinval.h because
+ * we'd have to include xlog.h into that ...
+ */
+extern XLogRecPtr GetUndoRecPtr(void);
+
#endif /* XLOG_H */
* Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
- * $Id: proc.h,v 1.39 2001/01/25 03:31:16 tgl Exp $
+ * $Id: proc.h,v 1.40 2001/02/26 00:50:08 tgl Exp $
*
*-------------------------------------------------------------------------
*/
* were starting our xact: vacuum must not
* remove tuples deleted by xid >= xmin ! */
+ /* XLOG location of first XLOG record written by this backend's current
+ * transaction. If backend is not in a transaction or hasn't yet modified
+ * anything, logRec.xrecoff is zero.
+ */
XLogRecPtr logRec;
/* Info about lock the process is currently waiting for, if any. */
* Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
- * $Id: sinval.h,v 1.17 2001/01/24 19:43:28 momjian Exp $
+ * $Id: sinval.h,v 1.18 2001/02/26 00:50:08 tgl Exp $
*
*-------------------------------------------------------------------------
*/
extern bool DatabaseHasActiveBackends(Oid databaseId, bool ignoreMyself);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern void GetXmaxRecent(TransactionId *XmaxRecent);
-
+extern int CountActiveBackends(void);
#endif /* SINVAL_H */
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