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Commit0174769

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Repair two problems with WAL logging of sequence nextvalI() ops, as
per recent pghackers discussion: force a new WAL record at first nextvalafter a checkpoint, and ensure that xlog is flushed to disk if a nextvalrecord is the only thing emitted by a transaction.
1 parent0b73fe1 commit0174769

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6 files changed

+147
-68
lines changed

6 files changed

+147
-68
lines changed

‎src/backend/access/transam/xact.c‎

Lines changed: 47 additions & 29 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 1.117 2002/03/06 06:09:21 momjian Exp $
11+
* $Header: /cvsroot/pgsql/src/backend/access/transam/xact.c,v 1.118 2002/03/15 19:20:29 tgl Exp $
1212
*
1313
* NOTES
1414
*Transaction aborts can now occur two ways:
@@ -546,32 +546,48 @@ RecordTransactionCommit(void)
546546
xid=GetCurrentTransactionId();
547547

548548
/*
549-
* We needn't write anything in xlog or clog if the transaction was
550-
* read-only, which we check by testing if it made any xlog entries.
549+
* We only need to log the commit in xlog and clog if the transaction made
550+
* any transaction-controlled XLOG entries. (Otherwise, its XID appears
551+
* nowhere in permanent storage, so no one will ever care if it
552+
* committed.) However, we must flush XLOG to disk if we made any XLOG
553+
* entries, whether in or out of transaction control. For example, if we
554+
* reported a nextval() result to the client, this ensures that any XLOG
555+
* record generated by nextval will hit the disk before we report the
556+
* transaction committed.
551557
*/
552-
if (MyLastRecPtr.xrecoff!=0)
558+
if (MyXactMadeXLogEntry)
553559
{
554-
XLogRecDatardata;
555-
xl_xact_commitxlrec;
556560
XLogRecPtrrecptr;
557561

558562
BufmgrCommit();
559563

560-
xlrec.xtime=time(NULL);
561-
rdata.buffer=InvalidBuffer;
562-
rdata.data= (char*) (&xlrec);
563-
rdata.len=SizeOfXactCommit;
564-
rdata.next=NULL;
565-
566564
START_CRIT_SECTION();
567565

568-
/*
569-
* SHOULD SAVE ARRAY OF RELFILENODE-s TO DROP
570-
*/
571-
recptr=XLogInsert(RM_XACT_ID,XLOG_XACT_COMMIT,&rdata);
566+
if (MyLastRecPtr.xrecoff!=0)
567+
{
568+
/* Need to emit a commit record */
569+
XLogRecDatardata;
570+
xl_xact_commitxlrec;
571+
572+
xlrec.xtime=time(NULL);
573+
rdata.buffer=InvalidBuffer;
574+
rdata.data= (char*) (&xlrec);
575+
rdata.len=SizeOfXactCommit;
576+
rdata.next=NULL;
577+
578+
/*
579+
* XXX SHOULD SAVE ARRAY OF RELFILENODE-s TO DROP
580+
*/
581+
recptr=XLogInsert(RM_XACT_ID,XLOG_XACT_COMMIT,&rdata);
582+
}
583+
else
584+
{
585+
/* Just flush through last record written by me */
586+
recptr=ProcLastRecEnd;
587+
}
572588

573589
/*
574-
* Sleep beforecommit! So we can flush more than one commit
590+
* Sleep beforeflush! So we can flush more than one commit
575591
* records per single fsync. (The idea is some other backend may
576592
* do the XLogFlush while we're sleeping. This needs work still,
577593
* because on most Unixen, the minimum select() delay is 10msec or
@@ -593,15 +609,17 @@ RecordTransactionCommit(void)
593609

594610
XLogFlush(recptr);
595611

596-
/* Break the chain of back-links in the XLOG records I output */
597-
MyLastRecPtr.xrecoff=0;
598-
599-
/* Mark the transaction committed in clog */
600-
TransactionIdCommit(xid);
612+
/* Mark the transaction committed in clog, if needed */
613+
if (MyLastRecPtr.xrecoff!=0)
614+
TransactionIdCommit(xid);
601615

602616
END_CRIT_SECTION();
603617
}
604618

619+
/* Break the chain of back-links in the XLOG records I output */
620+
MyLastRecPtr.xrecoff=0;
621+
MyXactMadeXLogEntry= false;
622+
605623
/* Show myself as out of the transaction in PROC array */
606624
MyProc->logRec.xrecoff=0;
607625

@@ -689,8 +707,11 @@ RecordTransactionAbort(void)
689707
TransactionIdxid=GetCurrentTransactionId();
690708

691709
/*
692-
* We needn't write anything in xlog or clog if the transaction was
693-
* read-only, which we check by testing if it made any xlog entries.
710+
* We only need to log the abort in xlog and clog if the transaction made
711+
* any transaction-controlled XLOG entries. (Otherwise, its XID appears
712+
* nowhere in permanent storage, so no one will ever care if it
713+
* committed.) We do not flush XLOG to disk in any case, since the
714+
* default assumption after a crash would be that we aborted, anyway.
694715
*
695716
* Extra check here is to catch case that we aborted partway through
696717
* RecordTransactionCommit ...
@@ -714,11 +735,6 @@ RecordTransactionAbort(void)
714735
*/
715736
recptr=XLogInsert(RM_XACT_ID,XLOG_XACT_ABORT,&rdata);
716737

717-
/*
718-
* There's no need for XLogFlush here, since the default
719-
* assumption would be that we aborted, anyway.
720-
*/
721-
722738
/* Mark the transaction aborted in clog */
723739
TransactionIdAbort(xid);
724740

@@ -727,6 +743,8 @@ RecordTransactionAbort(void)
727743

728744
/* Break the chain of back-links in the XLOG records I output */
729745
MyLastRecPtr.xrecoff=0;
746+
MyXactMadeXLogEntry= false;
747+
730748
/* Show myself as out of the transaction in PROC array */
731749
MyProc->logRec.xrecoff=0;
732750

‎src/backend/access/transam/xlog.c‎

Lines changed: 61 additions & 25 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-
* $Header: /cvsroot/pgsql/src/backend/access/transam/xlog.c,v 1.89 2002/03/06 06:09:22 momjian Exp $
10+
* $Header: /cvsroot/pgsql/src/backend/access/transam/xlog.c,v 1.90 2002/03/15 19:20:30 tgl Exp $
1111
*
1212
*-------------------------------------------------------------------------
1313
*/
@@ -131,27 +131,36 @@ boolInRecovery = false;
131131

132132
/*
133133
* MyLastRecPtr points to the start of the last XLOG record inserted by the
134-
* current transaction. If MyLastRecPtr.xrecoff == 0, thenwe are not in
135-
*a transaction or the transaction has notyetmade anyloggable changes.
134+
* current transaction. If MyLastRecPtr.xrecoff == 0, thenthe current
135+
*xact hasn'tyetinserted anytransaction-controlled XLOG records.
136136
*
137137
* Note that XLOG records inserted outside transaction control are not
138-
* reflected into MyLastRecPtr.
138+
* reflected into MyLastRecPtr. They do, however, cause MyXactMadeXLogEntry
139+
* to be set true. The latter can be used to test whether the current xact
140+
* made any loggable changes (including out-of-xact changes, such as
141+
* sequence updates).
139142
*/
140143
XLogRecPtrMyLastRecPtr= {0,0};
141144

145+
boolMyXactMadeXLogEntry= false;
146+
142147
/*
143148
* ProcLastRecPtr points to the start of the last XLOG record inserted by the
144149
* current backend. It is updated for all inserts, transaction-controlled
145-
* or not.
150+
* or not. ProcLastRecEnd is similar but points to end+1 of last record.
146151
*/
147152
staticXLogRecPtrProcLastRecPtr= {0,0};
148153

154+
XLogRecPtrProcLastRecEnd= {0,0};
155+
149156
/*
150157
* RedoRecPtr is this backend's local copy of the REDO record pointer
151158
* (which is almost but not quite the same as a pointer to the most recent
152159
* CHECKPOINT record).We update this from the shared-memory copy,
153160
* XLogCtl->Insert.RedoRecPtr, whenever we can safely do so (ie, when we
154-
* hold the Insert lock). See XLogInsert for details.
161+
* hold the Insert lock). See XLogInsert for details. We are also allowed
162+
* to update from XLogCtl->Insert.RedoRecPtr if we hold the info_lck;
163+
* see GetRedoRecPtr.
155164
*/
156165
staticXLogRecPtrRedoRecPtr;
157166

@@ -272,7 +281,8 @@ typedef struct XLogCtlData
272281
StartUpIDThisStartUpID;
273282

274283
/* This value is not protected by *any* lock... */
275-
XLogRecPtrRedoRecPtr;/* see SetRedoRecPtr/GetRedoRecPtr */
284+
/* see SetSavedRedoRecPtr/GetSavedRedoRecPtr */
285+
XLogRecPtrSavedRedoRecPtr;
276286

277287
slock_tinfo_lck;/* locks shared LogwrtRqst/LogwrtResult */
278288
}XLogCtlData;
@@ -777,6 +787,7 @@ begin:;
777787
MyLastRecPtr=RecPtr;
778788
ProcLastRecPtr=RecPtr;
779789
Insert->PrevRecord=RecPtr;
790+
MyXactMadeXLogEntry= true;
780791

781792
Insert->currpos+=SizeOfXLogRecord;
782793
freespace-=SizeOfXLogRecord;
@@ -855,6 +866,8 @@ begin:;
855866
SpinLockRelease_NoHoldoff(&xlogctl->info_lck);
856867
}
857868

869+
ProcLastRecEnd=RecPtr;
870+
858871
END_CRIT_SECTION();
859872

860873
return (RecPtr);
@@ -2538,7 +2551,7 @@ StartupXLOG(void)
25382551

25392552
ThisStartUpID=checkPoint.ThisStartUpID;
25402553
RedoRecPtr=XLogCtl->Insert.RedoRecPtr=
2541-
XLogCtl->RedoRecPtr=checkPoint.redo;
2554+
XLogCtl->SavedRedoRecPtr=checkPoint.redo;
25422555

25432556
if (XLByteLT(RecPtr,checkPoint.redo))
25442557
elog(PANIC,"invalid redo in checkpoint record");
@@ -2824,32 +2837,47 @@ void
28242837
SetThisStartUpID(void)
28252838
{
28262839
ThisStartUpID=XLogCtl->ThisStartUpID;
2827-
RedoRecPtr=XLogCtl->RedoRecPtr;
2840+
RedoRecPtr=XLogCtl->SavedRedoRecPtr;
28282841
}
28292842

28302843
/*
28312844
* CheckPoint process called by postmaster saves copy of new RedoRecPtr
2832-
* in shmem (using SetRedoRecPtr).When checkpointer completes, postmaster
2833-
* calls GetRedoRecPtr to update its own copy of RedoRecPtr, so that
2834-
* subsequently-spawned backends will start out with a reasonably up-to-date
2835-
* local RedoRecPtr. Since these operations are not protected by any lock
2836-
* and copying an XLogRecPtr isn't atomic, it's unsafe to use either of these
2837-
* routines at other times!
2838-
*
2839-
* Note: once spawned, a backend must update its local RedoRecPtr from
2840-
* XLogCtl->Insert.RedoRecPtr while holding the insert lock. This is
2841-
* done in XLogInsert().
2845+
* in shmem (using SetSavedRedoRecPtr). When checkpointer completes,
2846+
* postmaster calls GetSavedRedoRecPtr to update its own copy of RedoRecPtr,
2847+
* so that subsequently-spawned backends will start out with a reasonably
2848+
* up-to-date local RedoRecPtr. Since these operations are not protected by
2849+
* any lock and copying an XLogRecPtr isn't atomic, it's unsafe to use either
2850+
* of these routines at other times!
28422851
*/
28432852
void
2844-
SetRedoRecPtr(void)
2853+
SetSavedRedoRecPtr(void)
28452854
{
2846-
XLogCtl->RedoRecPtr=RedoRecPtr;
2855+
XLogCtl->SavedRedoRecPtr=RedoRecPtr;
28472856
}
28482857

28492858
void
2859+
GetSavedRedoRecPtr(void)
2860+
{
2861+
RedoRecPtr=XLogCtl->SavedRedoRecPtr;
2862+
}
2863+
2864+
/*
2865+
* Once spawned, a backend may update its local RedoRecPtr from
2866+
* XLogCtl->Insert.RedoRecPtr; it must hold the insert lock or info_lck
2867+
* to do so. This is done in XLogInsert() or GetRedoRecPtr().
2868+
*/
2869+
XLogRecPtr
28502870
GetRedoRecPtr(void)
28512871
{
2852-
RedoRecPtr=XLogCtl->RedoRecPtr;
2872+
/* use volatile pointer to prevent code rearrangement */
2873+
volatileXLogCtlData*xlogctl=XLogCtl;
2874+
2875+
SpinLockAcquire_NoHoldoff(&xlogctl->info_lck);
2876+
Assert(XLByteLE(RedoRecPtr,xlogctl->Insert.RedoRecPtr));
2877+
RedoRecPtr=xlogctl->Insert.RedoRecPtr;
2878+
SpinLockRelease_NoHoldoff(&xlogctl->info_lck);
2879+
2880+
returnRedoRecPtr;
28532881
}
28542882

28552883
/*
@@ -2862,6 +2890,7 @@ ShutdownXLOG(void)
28622890

28632891
/* suppress in-transaction check in CreateCheckPoint */
28642892
MyLastRecPtr.xrecoff=0;
2893+
MyXactMadeXLogEntry= false;
28652894

28662895
CritSectionCount++;
28672896
CreateDummyCaches();
@@ -2886,7 +2915,7 @@ CreateCheckPoint(bool shutdown)
28862915
uint32_logId;
28872916
uint32_logSeg;
28882917

2889-
if (MyLastRecPtr.xrecoff!=0)
2918+
if (MyXactMadeXLogEntry)
28902919
elog(ERROR,"CreateCheckPoint: cannot be called inside transaction block");
28912920

28922921
/*
@@ -2972,9 +3001,16 @@ CreateCheckPoint(bool shutdown)
29723001

29733002
/*
29743003
* Here we update the shared RedoRecPtr for future XLogInsert calls;
2975-
* this must be done while holding the insert lock.
3004+
* this must be done while holding the insert lock AND the info_lck.
29763005
*/
2977-
RedoRecPtr=XLogCtl->Insert.RedoRecPtr=checkPoint.redo;
3006+
{
3007+
/* use volatile pointer to prevent code rearrangement */
3008+
volatileXLogCtlData*xlogctl=XLogCtl;
3009+
3010+
SpinLockAcquire_NoHoldoff(&xlogctl->info_lck);
3011+
RedoRecPtr=xlogctl->Insert.RedoRecPtr=checkPoint.redo;
3012+
SpinLockRelease_NoHoldoff(&xlogctl->info_lck);
3013+
}
29783014

29793015
/*
29803016
* Get UNDO record ptr - this is oldest of PROC->logRec values. We do

‎src/backend/bootstrap/bootstrap.c‎

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
* Portions Copyright (c) 1994, Regents of the University of California
99
*
1010
* IDENTIFICATION
11-
* $Header: /cvsroot/pgsql/src/backend/bootstrap/bootstrap.c,v 1.123 2002/03/08 00:42:09 tgl Exp $
11+
* $Header: /cvsroot/pgsql/src/backend/bootstrap/bootstrap.c,v 1.124 2002/03/15 19:20:34 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -386,7 +386,7 @@ BootstrapMain(int argc, char *argv[])
386386
InitDummyProcess();/* needed to get LWLocks */
387387
CreateDummyCaches();
388388
CreateCheckPoint(false);
389-
SetRedoRecPtr();
389+
SetSavedRedoRecPtr();/* pass redo ptr back to postmaster */
390390
proc_exit(0);/* done */
391391

392392
caseBS_XLOG_STARTUP:

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