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Commitc186ba1

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Ensure correct minimum consistent point on standbys
Startup process has improved its calculation of incorrect minimumconsistent point in8d68ee6, which ensures that all WAL available getsreplayed when doing crash recovery, and has introduced an incorrectcalculation of the minimum recovery point for non-startup processes,which can cause incorrect page references on a standby when for examplethe background writer flushed a couple of pages on-disk but was notupdating the control file to let a subsequent crash recovery replay towhere it should have.The only case where this has been reported to be a problem is when astandby needs to calculate the latest removed xid when replaying a btreedeletion record, so one would need connections on a standby that happenjust after recovery has thought it reached a consistent point. Using abackground worker which is started after the consistent point is reachedwould be the easiest way to get into problems if it connects to adatabase. Having clients which attempt to connect periodically couldalso be a problem, but the odds of seeing this problem are much lower.The fix used is pretty simple, as the idea is to give access to theminimum recovery point written in the control file to non-startupprocesses so as they use a reference, while the startup process stillinitializes its own references of the minimum consistent point so as theoriginal problem with incorrect page references happening post-promotionwith a crash do not show up.Reported-by: Alexander KukushkinDiagnosed-by: Alexander KukushkinAuthor: Michael PaquierReviewed-by: Kyotaro Horiguchi, Alexander KukushkinDiscussion:https://postgr.es/m/153492341830.1368.3936905691758473953@wrigleys.postgresql.orgBackpatch-through: 9.3
1 parentd9c366f commitc186ba1

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1 file changed

+25
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lines changed
  • src/backend/access/transam

1 file changed

+25
-6
lines changed

‎src/backend/access/transam/xlog.c

Lines changed: 25 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -2723,9 +2723,13 @@ UpdateMinRecoveryPoint(XLogRecPtr lsn, bool force)
27232723
* i.e., we're doing crash recovery. We never modify the control file's
27242724
* value in that case, so we can short-circuit future checks here too. The
27252725
* local values of minRecoveryPoint and minRecoveryPointTLI should not be
2726-
* updated until crash recovery finishes.
2726+
* updated until crash recovery finishes. We only do this for the startup
2727+
* process as it should not update its own reference of minRecoveryPoint
2728+
* until it has finished crash recovery to make sure that all WAL
2729+
* available is replayed in this case. This also saves from extra locks
2730+
* taken on the control file from the startup process.
27272731
*/
2728-
if (XLogRecPtrIsInvalid(minRecoveryPoint))
2732+
if (XLogRecPtrIsInvalid(minRecoveryPoint)&&InRecovery)
27292733
{
27302734
updateMinRecoveryPoint= false;
27312735
return;
@@ -2737,7 +2741,9 @@ UpdateMinRecoveryPoint(XLogRecPtr lsn, bool force)
27372741
minRecoveryPoint=ControlFile->minRecoveryPoint;
27382742
minRecoveryPointTLI=ControlFile->minRecoveryPointTLI;
27392743

2740-
if (force||minRecoveryPoint<lsn)
2744+
if (XLogRecPtrIsInvalid(minRecoveryPoint))
2745+
updateMinRecoveryPoint= false;
2746+
elseif (force||minRecoveryPoint<lsn)
27412747
{
27422748
XLogRecPtrnewMinRecoveryPoint;
27432749
TimeLineIDnewMinRecoveryPointTLI;
@@ -3127,9 +3133,11 @@ XLogNeedsFlush(XLogRecPtr record)
31273133
* An invalid minRecoveryPoint means that we need to recover all the
31283134
* WAL, i.e., we're doing crash recovery. We never modify the control
31293135
* file's value in that case, so we can short-circuit future checks
3130-
* here too.
3136+
* here too. This triggers a quick exit path for the startup process,
3137+
* which cannot update its local copy of minRecoveryPoint as long as
3138+
* it has not replayed all WAL available when doing crash recovery.
31313139
*/
3132-
if (XLogRecPtrIsInvalid(minRecoveryPoint))
3140+
if (XLogRecPtrIsInvalid(minRecoveryPoint)&&InRecovery)
31333141
updateMinRecoveryPoint= false;
31343142

31353143
/* Quick exit if already known to be updated or cannot be updated */
@@ -3146,8 +3154,19 @@ XLogNeedsFlush(XLogRecPtr record)
31463154
minRecoveryPointTLI=ControlFile->minRecoveryPointTLI;
31473155
LWLockRelease(ControlFileLock);
31483156

3157+
/*
3158+
* Check minRecoveryPoint for any other process than the startup
3159+
* process doing crash recovery, which should not update the control
3160+
* file value if crash recovery is still running.
3161+
*/
3162+
if (XLogRecPtrIsInvalid(minRecoveryPoint))
3163+
updateMinRecoveryPoint= false;
3164+
31493165
/* check again */
3150-
returnrecord>minRecoveryPoint;
3166+
if (record <=minRecoveryPoint|| !updateMinRecoveryPoint)
3167+
return false;
3168+
else
3169+
return true;
31513170
}
31523171

31533172
/* Quick exit if already known flushed */

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