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Commitf44eedc

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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 parent4f1490c commitf44eedc

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3 files changed

+48
-4
lines changed

3 files changed

+48
-4
lines changed

‎src/backend/access/transam/xlog.c

Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -6117,6 +6117,9 @@ StartupXLOG(void)
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oldestActiveXID=checkPoint.oldestActiveXid;
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Assert(TransactionIdIsValid(oldestActiveXID));
61196119

6120+
/* Tell procarray about the range of xids it has to deal with */
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ProcArrayInitRecovery(ShmemVariableCache->nextXid);
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/*
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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: 44 additions & 4 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

438+
/*
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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
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ProcArrayInitRecovery(TransactionIdinitializedUptoXID)
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{
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Assert(standbyState==STANDBY_INITIALIZED);
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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
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* 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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/*
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* ProcArrayApplyRecoveryInfo -- apply recovery info about xids
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*
@@ -523,7 +545,10 @@ ProcArrayApplyRecoveryInfo(RunningTransactions running)
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Assert(standbyState==STANDBY_INITIALIZED);
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/*
526-
* OK, we need to initialise from the RunningTransactionsData record
548+
* OK, we need to initialise from the RunningTransactionsData record.
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*
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* NB: this can be reached at least twice, so make sure new code can deal
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* with that.
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*/
528553

529554
/*
@@ -595,6 +620,19 @@ ProcArrayApplyRecoveryInfo(RunningTransactions running)
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pfree(xids);
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/*
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* latestObservedXid is set to the the point where SUBTRANS was started up
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* to, initialize subtrans from thereon, up to nextXid - 1.
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*/
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Assert(TransactionIdIsNormal(latestObservedXid));
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while (TransactionIdPrecedes(latestObservedXid,running->nextXid))
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{
629+
ExtendCLOG(latestObservedXid);
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ExtendSUBTRANS(latestObservedXid);
631+
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TransactionIdAdvance(latestObservedXid);
633+
}
634+
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/* ----------
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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
*
@@ -606,10 +644,8 @@ ProcArrayApplyRecoveryInfo(RunningTransactions running)
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* but the recovery snapshot isn't fully valid yet because we know there
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* are some subxids missing. We don't know the specific subxids that are
608646
* missing, so conservatively assume the last one is latestObservedXid.
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* ----------
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*/
610-
latestObservedXid=running->nextXid;
611-
TransactionIdRetreat(latestObservedXid);
612-
613649
if (running->subxid_overflow)
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{
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standbyState=STANDBY_SNAPSHOT_PENDING;
@@ -669,6 +705,10 @@ ProcArrayApplyXidAssignment(TransactionId topxid,
669705

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Assert(standbyState >=STANDBY_INITIALIZED);
671707

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/* can't do anything useful unless we have more state setup */
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if (standbyState==STANDBY_INITIALIZED)
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return;
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max_xid=TransactionIdLatest(topxid,nsubxids,subxids);
673713

674714
/*

‎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);
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externvoidProcArrayEndTransaction(PGPROC*proc,TransactionIdlatestXid);
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externvoidProcArrayClearTransaction(PGPROC*proc);
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31+
externvoidProcArrayInitRecovery(TransactionIdinitializedUptoXID);
3132
externvoidProcArrayApplyRecoveryInfo(RunningTransactionsrunning);
3233
externvoidProcArrayApplyXidAssignment(TransactionIdtopxid,
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intnsubxids,TransactionId*subxids);

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