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Commita41c881

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Ensure no xid gaps during Hot Standby startup
In some cases with higher numbers of subtransactionsit was possible for us to incorrectly initializesubtrans leading to complaints of missing pages.Bug report by Sergey KonoplevAnalysis and fix by Andres Freund
1 parent27e9e86 commita41c881

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3 files changed

+51
-6
lines changed

3 files changed

+51
-6
lines changed

‎src/backend/access/transam/xlog.c‎

Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -6449,6 +6449,9 @@ StartupXLOG(void)
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oldestActiveXID=checkPoint.oldestActiveXid;
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Assert(TransactionIdIsValid(oldestActiveXID));
64516451

6452+
/* Tell procarray about the range of xids it has to deal with */
6453+
ProcArrayInitRecovery(ShmemVariableCache->nextXid);
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64526455
/*
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* Startup commit log and subtrans only. Other SLRUs are not
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* maintained during recovery and need not be started yet.

‎src/backend/storage/ipc/procarray.c‎

Lines changed: 47 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -435,6 +435,28 @@ ProcArrayClearTransaction(PGPROC *proc)
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proc->subxids.overflowed= false;
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}
437437

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/*
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* ProcArrayInitRecovery -- initialize recovery xid mgmt environment
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*
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* Remember up to where the startup process initialized the CLOG and subtrans
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* so we can ensure its initialized gaplessly up to the point where necessary
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* while in recovery.
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*/
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void
446+
ProcArrayInitRecovery(TransactionIdinitializedUptoXID)
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{
448+
Assert(standbyState==STANDBY_INITIALIZED);
449+
Assert(TransactionIdIsNormal(initializedUptoXID));
450+
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/*
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* we set latestObservedXid to the xid SUBTRANS has been initialized upto
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* so we can extend it from that point onwards when we reach a consistent
454+
* state in ProcArrayApplyRecoveryInfo().
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*/
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latestObservedXid=initializedUptoXID;
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TransactionIdRetreat(latestObservedXid);
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}
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438460
/*
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* ProcArrayApplyRecoveryInfo -- apply recovery info about xids
440462
*
@@ -523,7 +545,10 @@ ProcArrayApplyRecoveryInfo(RunningTransactions running)
523545
Assert(standbyState==STANDBY_INITIALIZED);
524546

525547
/*
526-
* OK, we need to initialise from the RunningTransactionsData record
548+
* OK, we need to initialise from the RunningTransactionsData record.
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*
550+
* NB: this can be reached at least twice, so make sure new code can deal
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* with that.
527552
*/
528553

529554
/*
@@ -595,20 +620,32 @@ ProcArrayApplyRecoveryInfo(RunningTransactions running)
595620
pfree(xids);
596621

597622
/*
623+
* latestObservedXid is set to the the point where SUBTRANS was started up
624+
* to, initialize subtrans from thereon, up to nextXid - 1.
625+
*/
626+
Assert(TransactionIdIsNormal(latestObservedXid));
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while (TransactionIdPrecedes(latestObservedXid,running->nextXid))
628+
{
629+
ExtendCLOG(latestObservedXid);
630+
ExtendSUBTRANS(latestObservedXid);
631+
632+
TransactionIdAdvance(latestObservedXid);
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}
634+
635+
/* ----------
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* Now we've got the running xids we need to set the global values that
599637
* are used to track snapshots as they evolve further.
600638
*
601-
* - latestCompletedXid which will be the xmax for snapshots -
602-
* lastOverflowedXid which shows whether snapshots overflow - nextXid
639+
* - latestCompletedXid which will be the xmax for snapshots
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* - lastOverflowedXid which shows whether snapshots overflow
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* - nextXid
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*
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* If the snapshot overflowed, then we still initialise with what we know,
605644
* but the recovery snapshot isn't fully valid yet because we know there
606645
* are some subxids missing. We don't know the specific subxids that are
607646
* missing, so conservatively assume the last one is latestObservedXid.
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* ----------
608648
*/
609-
latestObservedXid=running->nextXid;
610-
TransactionIdRetreat(latestObservedXid);
611-
612649
if (running->subxid_overflow)
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{
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standbyState=STANDBY_SNAPSHOT_PENDING;
@@ -667,6 +704,10 @@ ProcArrayApplyXidAssignment(TransactionId topxid,
667704

668705
Assert(standbyState >=STANDBY_INITIALIZED);
669706

707+
/* can't do anything useful unless we have more state setup */
708+
if (standbyState==STANDBY_INITIALIZED)
709+
return;
710+
670711
max_xid=TransactionIdLatest(topxid,nsubxids,subxids);
671712

672713
/*

‎src/include/storage/procarray.h‎

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -28,6 +28,7 @@ extern void ProcArrayRemove(PGPROC *proc, TransactionId latestXid);
2828
externvoidProcArrayEndTransaction(PGPROC*proc,TransactionIdlatestXid);
2929
externvoidProcArrayClearTransaction(PGPROC*proc);
3030

31+
externvoidProcArrayInitRecovery(TransactionIdinitializedUptoXID);
3132
externvoidProcArrayApplyRecoveryInfo(RunningTransactionsrunning);
3233
externvoidProcArrayApplyXidAssignment(TransactionIdtopxid,
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intnsubxids,TransactionId*subxids);

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