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Implement COMMIT_SIBLINGS parameter to allow pre-commit delay to occur
only if at least N other backends currently have open transactions. This is not a great deal of intelligence about whether a delay might be profitable ... but it beats no intelligence at all. Note that the default COMMIT_DELAY is still zero --- this new code does nothing unless that setting is changed. Also, mark ENABLEFSYNC as a system-wide setting. It's no longer safe to allow that to be set per-backend, since we may be relying on some other backend's fsync to have synced the WAL log.
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10 files changed

+94
-31
lines changed

10 files changed

+94
-31
lines changed

‎doc/src/sgml/wal.sgml

Lines changed: 8 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -1,4 +1,4 @@
1-
<!-- $Header: /cvsroot/pgsql/doc/src/sgml/wal.sgml,v 1.2 2001/02/18 04:50:43 tgl Exp $ -->
1+
<!-- $Header: /cvsroot/pgsql/doc/src/sgml/wal.sgml,v 1.3 2001/02/26 00:50:07 tgl Exp $ -->
22

33
<chapter id="wal">
44
<title>Write-Ahead Logging (<acronym>WAL</acronym>)</title>
@@ -295,10 +295,13 @@
295295
record to the log with <function>LogInsert</function> but before
296296
performing a <function>LogFlush</function>. This delay allows other
297297
backends to add their commit records to the log so as to have all
298-
of them flushed with a single log sync. Unfortunately, this
299-
mechanism is not fully implemented at release 7.1, so there is at
300-
present usually no benefit to be gained from increasing this parameter
301-
above its default value of zero.
298+
of them flushed with a single log sync. No sleep will occur if fsync
299+
is not enabled or if fewer than <varname>COMMIT_SIBLINGS</varname>
300+
other backends are not currently in active transactions; this avoids
301+
sleeping when it's unlikely that any other backend will commit soon.
302+
Note that on most platforms, the resolution of a sleep request is
303+
ten milliseconds, so that any nonzero <varname>COMMIT_DELAY</varname>
304+
setting between 1 and 10000 microseconds will have the same effect.
302305
</para>
303306
</sect1>
304307
</chapter>

‎src/backend/access/transam/xact.c

Lines changed: 14 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $Header: /cvsroot/pgsql/src/backend/access/transam/xact.c,v 1.97 2001/02/18 04:50:43 tgl Exp $
11+
* $Header: /cvsroot/pgsql/src/backend/access/transam/xact.c,v 1.98 2001/02/26 00:50:07 tgl Exp $
1212
*
1313
* NOTES
1414
* Transaction aborts can now occur two ways:
@@ -157,6 +157,7 @@
157157
#include <sys/time.h>
158158

159159
#include "access/nbtree.h"
160+
#include "access/xact.h"
160161
#include "catalog/heap.h"
161162
#include "catalog/index.h"
162163
#include "commands/async.h"
@@ -177,8 +178,6 @@
177178

178179
extern bool SharedBufferChanged;
179180

180-
void RecordTransactionCommit(void);
181-
182181
static void AbortTransaction(void);
183182
static void AtAbort_Cache(void);
184183
static void AtAbort_Locks(void);
@@ -216,12 +215,14 @@ TransactionStateData CurrentTransactionStateData = {
216215

217216
TransactionState CurrentTransactionState = &CurrentTransactionStateData;
218217

218+
/*
219+
* User-tweakable parameters
220+
*/
219221
int DefaultXactIsoLevel = XACT_READ_COMMITTED;
220222
int XactIsoLevel;
221223

222-
#include "access/xlogutils.h"
223-
224-
int CommitDelay = 0; /* in microseconds */
224+
int CommitDelay = 0; /* precommit delay in microseconds */
225+
int CommitSiblings = 5; /* number of concurrent xacts needed to sleep */
225226

226227
static void (*_RollbackFunc)(void*) = NULL;
227228
static void *_RollbackData = NULL;
@@ -687,10 +688,15 @@ RecordTransactionCommit()
687688
* Sleep before commit! So we can flush more than one
688689
* commit records per single fsync. (The idea is some other
689690
* backend may do the XLogFlush while we're sleeping. This
690-
* needs work however, because on most Unixen, the minimum
691+
* needs work still, because on most Unixen, the minimum
691692
* select() delay is 10msec or more, which is way too long.)
693+
*
694+
* We do not sleep if enableFsync is not turned on, nor if there
695+
* are fewer than CommitSiblings other backends with active
696+
* transactions.
692697
*/
693-
if (CommitDelay > 0)
698+
if (CommitDelay > 0 && enableFsync &&
699+
CountActiveBackends() >= CommitSiblings)
694700
{
695701
struct timeval delay;
696702

‎src/backend/access/transam/xlog.c

Lines changed: 1 addition & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -6,7 +6,7 @@
66
* Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
77
* Portions Copyright (c) 1994, Regents of the University of California
88
*
9-
* $Header: /cvsroot/pgsql/src/backend/access/transam/xlog.c,v 1.54 2001/02/18 04:39:42 tgl Exp $
9+
* $Header: /cvsroot/pgsql/src/backend/access/transam/xlog.c,v 1.55 2001/02/26 00:50:07 tgl Exp $
1010
*
1111
*-------------------------------------------------------------------------
1212
*/
@@ -2096,8 +2096,6 @@ ShutdownXLOG()
20962096
elog(LOG, "database system is shut down");
20972097
}
20982098

2099-
extern XLogRecPtr GetUndoRecPtr(void);
2100-
21012099
void
21022100
CreateCheckPoint(bool shutdown)
21032101
{

‎src/backend/storage/ipc/sinval.c

Lines changed: 47 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -8,16 +8,14 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $Header: /cvsroot/pgsql/src/backend/storage/ipc/sinval.c,v 1.25 2001/01/24 19:43:07 momjian Exp $
11+
* $Header: /cvsroot/pgsql/src/backend/storage/ipc/sinval.c,v 1.26 2001/02/26 00:50:07 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
15-
/* #define INVALIDDEBUG 1 */
15+
#include "postgres.h"
1616

1717
#include <sys/types.h>
1818

19-
#include "postgres.h"
20-
2119
#include "storage/backendid.h"
2220
#include "storage/proc.h"
2321
#include "storage/sinval.h"
@@ -348,10 +346,53 @@ GetSnapshotData(bool serializable)
348346
}
349347

350348
/*
351-
* GetUndoRecPtr -- returns oldest PROC->logRec.
349+
* CountActiveBackends --- count backends (other than myself) that are in
350+
* active transactions. This is used as a heuristic to decide if
351+
* a pre-XLOG-flush delay is worthwhile during commit.
352+
*
353+
* An active transaction is something that has written at least one XLOG
354+
* record; read-only transactions don't count. Also, do not count backends
355+
* that are blocked waiting for locks, since they are not going to get to
356+
* run until someone else commits.
352357
*/
353-
XLogRecPtr GetUndoRecPtr(void);
358+
int
359+
CountActiveBackends(void)
360+
{
361+
SISeg *segP = shmInvalBuffer;
362+
ProcState *stateP = segP->procState;
363+
int count = 0;
364+
int index;
354365

366+
/*
367+
* Note: for speed, we don't acquire SInvalLock. This is a little bit
368+
* bogus, but since we are only testing xrecoff for zero or nonzero,
369+
* it should be OK. The result is only used for heuristic purposes
370+
* anyway...
371+
*/
372+
for (index = 0; index < segP->lastBackend; index++)
373+
{
374+
SHMEM_OFFSET pOffset = stateP[index].procStruct;
375+
376+
if (pOffset != INVALID_OFFSET)
377+
{
378+
PROC *proc = (PROC *) MAKE_PTR(pOffset);
379+
380+
if (proc == MyProc)
381+
continue; /* do not count myself */
382+
if (proc->logRec.xrecoff == 0)
383+
continue; /* do not count if not in a transaction */
384+
if (proc->waitLock != NULL)
385+
continue; /* do not count if blocked on a lock */
386+
count++;
387+
}
388+
}
389+
390+
return count;
391+
}
392+
393+
/*
394+
* GetUndoRecPtr -- returns oldest PROC->logRec.
395+
*/
355396
XLogRecPtr
356397
GetUndoRecPtr(void)
357398
{

‎src/backend/utils/misc/guc.c

Lines changed: 7 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -4,7 +4,7 @@
44
* Support for grand unified configuration scheme, including SET
55
* command, configuration file, and command line options.
66
*
7-
* $Header: /cvsroot/pgsql/src/backend/utils/misc/guc.c,v 1.30 2001/02/18 04:50:43 tgl Exp $
7+
* $Header: /cvsroot/pgsql/src/backend/utils/misc/guc.c,v 1.31 2001/02/26 00:50:07 tgl Exp $
88
*
99
* Copyright 2000 by PostgreSQL Global Development Group
1010
* Written by Peter Eisentraut <peter_e@gmx.net>.
@@ -41,6 +41,7 @@ extern int XLOGbuffers;
4141
extern int XLOGfiles;
4242
extern int XLOG_DEBUG;
4343
extern int CommitDelay;
44+
extern int CommitSiblings;
4445

4546
extern bool FixBTree;
4647

@@ -181,7 +182,7 @@ ConfigureNamesBool[] =
181182

182183
{"tcpip_socket", PGC_POSTMASTER, &NetServer, false},
183184
{"ssl", PGC_POSTMASTER, &EnableSSL, false},
184-
{"fsync", PGC_USERSET, &enableFsync, true},
185+
{"fsync", PGC_SIGHUP, &enableFsync, true},
185186
{"silent_mode", PGC_POSTMASTER, &SilentMode, false},
186187

187188
{"log_connections", PGC_SIGHUP, &Log_connections, false},
@@ -279,7 +280,7 @@ ConfigureNamesInt[] =
279280
0777, 0000, 0777},
280281

281282
{"checkpoint_timeout", PGC_POSTMASTER, &CheckPointTimeout,
282-
300, 30, 1800},
283+
300, 30, 3600},
283284

284285
{"wal_buffers", PGC_POSTMASTER, &XLOGbuffers,
285286
8, 4, INT_MAX},
@@ -293,6 +294,9 @@ ConfigureNamesInt[] =
293294
{"commit_delay", PGC_USERSET, &CommitDelay,
294295
0, 0, 100000},
295296

297+
{"commit_siblings", PGC_USERSET, &CommitSiblings,
298+
5, 1, 1000},
299+
296300
{NULL, 0, NULL, 0, 0, 0}
297301
};
298302

‎src/backend/utils/misc/postgresql.conf.sample

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -109,7 +109,8 @@
109109
#wal_files = 0 # range 0-64
110110
#wal_debug = 0 # range 0-16
111111
#commit_delay = 0 # range 0-100000
112-
#checkpoint_timeout = 300 # range 30-1800
112+
#commit_siblings = 5 # range 1-1000
113+
#checkpoint_timeout = 300 # in seconds, range 30-3600
113114

114115

115116
#

‎src/bin/psql/tab-complete.c

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -3,7 +3,7 @@
33
*
44
* Copyright 2000 by PostgreSQL Global Development Group
55
*
6-
* $Header: /cvsroot/pgsql/src/bin/psql/tab-complete.c,v 1.26 2001/02/10 02:31:28 tgl Exp $
6+
* $Header: /cvsroot/pgsql/src/bin/psql/tab-complete.c,v 1.27 2001/02/26 00:50:07 tgl Exp $
77
*/
88

99
/*----------------------------------------------------------------------
@@ -241,6 +241,7 @@ psql_completion(char *text, int start, int end)
241241
"debug_level",
242242
"max_expr_depth",
243243
"commit_delay",
244+
"commit_siblings",
244245

245246
"effective_cache_size",
246247
"random_page_cost",

‎src/include/access/xlog.h

Lines changed: 6 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -3,7 +3,7 @@
33
*
44
* PostgreSQL transaction log manager
55
*
6-
* $Header: /cvsroot/pgsql/src/include/access/xlog.h,v 1.17 2001/01/14 05:08:16 tgl Exp $
6+
* $Header: /cvsroot/pgsql/src/include/access/xlog.h,v 1.18 2001/02/26 00:50:07 tgl Exp $
77
*/
88
#ifndef XLOG_H
99
#define XLOG_H
@@ -146,4 +146,9 @@ extern void ShutdownXLOG(void);
146146
extern void CreateCheckPoint(bool shutdown);
147147
extern void SetThisStartUpID(void);
148148

149+
/* in storage/ipc/sinval.c, but don't want to declare in sinval.h because
150+
* we'd have to include xlog.h into that ...
151+
*/
152+
extern XLogRecPtr GetUndoRecPtr(void);
153+
149154
#endif /* XLOG_H */

‎src/include/storage/proc.h

Lines changed: 5 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@
77
* Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
88
* Portions Copyright (c) 1994, Regents of the University of California
99
*
10-
* $Id: proc.h,v 1.39 2001/01/25 03:31:16 tgl Exp $
10+
* $Id: proc.h,v 1.40 2001/02/26 00:50:08 tgl Exp $
1111
*
1212
*-------------------------------------------------------------------------
1313
*/
@@ -50,6 +50,10 @@ struct proc
5050
* were starting our xact: vacuum must not
5151
* remove tuples deleted by xid >= xmin ! */
5252

53+
/* XLOG location of first XLOG record written by this backend's current
54+
* transaction. If backend is not in a transaction or hasn't yet modified
55+
* anything, logRec.xrecoff is zero.
56+
*/
5357
XLogRecPtr logRec;
5458

5559
/* Info about lock the process is currently waiting for, if any. */

‎src/include/storage/sinval.h

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@
77
* Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
88
* Portions Copyright (c) 1994, Regents of the University of California
99
*
10-
* $Id: sinval.h,v 1.17 2001/01/24 19:43:28 momjian Exp $
10+
* $Id: sinval.h,v 1.18 2001/02/26 00:50:08 tgl Exp $
1111
*
1212
*-------------------------------------------------------------------------
1313
*/
@@ -30,6 +30,6 @@ extern void InvalidateSharedInvalid(void (*invalFunction) (),
3030
extern bool DatabaseHasActiveBackends(Oid databaseId, bool ignoreMyself);
3131
extern bool TransactionIdIsInProgress(TransactionId xid);
3232
extern void GetXmaxRecent(TransactionId *XmaxRecent);
33-
33+
extern int CountActiveBackends(void);
3434

3535
#endif /* SINVAL_H */

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