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Commit99ee15b

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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 parent73c103d commit99ee15b

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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
@@ -6692,6 +6692,9 @@ StartupXLOG(void)
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oldestActiveXID=checkPoint.oldestActiveXid;
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Assert(TransactionIdIsValid(oldestActiveXID));
66946694

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/* Tell procarray about the range of xids it has to deal with */
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ProcArrayInitRecovery(ShmemVariableCache->nextXid);
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66956698
/*
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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
@@ -468,6 +468,28 @@ ProcArrayClearTransaction(PGPROC *proc)
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pgxact->overflowed= false;
469469
}
470470

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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
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ProcArrayInitRecovery(TransactionIdinitializedUptoXID)
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{
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Assert(standbyState==STANDBY_INITIALIZED);
482+
Assert(TransactionIdIsNormal(initializedUptoXID));
483+
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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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*
@@ -556,7 +578,10 @@ ProcArrayApplyRecoveryInfo(RunningTransactions running)
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Assert(standbyState==STANDBY_INITIALIZED);
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558580
/*
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* OK, we need to initialise from the RunningTransactionsData record
581+
* 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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*/
561586

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/*
@@ -628,20 +653,32 @@ ProcArrayApplyRecoveryInfo(RunningTransactions running)
628653
pfree(xids);
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630655
/*
656+
* latestObservedXid is set to the the point where SUBTRANS was started up
657+
* 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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{
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ExtendCLOG(latestObservedXid);
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ExtendSUBTRANS(latestObservedXid);
664+
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TransactionIdAdvance(latestObservedXid);
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}
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/* ----------
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* Now we've got the running xids we need to set the global values that
632670
* are used to track snapshots as they evolve further.
633671
*
634-
* - latestCompletedXid which will be the xmax for snapshots -
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* lastOverflowedXid which shows whether snapshots overflow - nextXid
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* - 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,
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* but the recovery snapshot isn't fully valid yet because we know there
639678
* are some subxids missing. We don't know the specific subxids that are
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* missing, so conservatively assume the last one is latestObservedXid.
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* ----------
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*/
642-
latestObservedXid=running->nextXid;
643-
TransactionIdRetreat(latestObservedXid);
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if (running->subxid_overflow)
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{
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standbyState=STANDBY_SNAPSHOT_PENDING;
@@ -711,6 +748,10 @@ ProcArrayApplyXidAssignment(TransactionId topxid,
711748

712749
Assert(standbyState >=STANDBY_INITIALIZED);
713750

751+
/* 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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714755
max_xid=TransactionIdLatest(topxid,nsubxids,subxids);
715756

716757
/*

‎src/include/storage/procarray.h‎

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -26,6 +26,7 @@ extern void ProcArrayRemove(PGPROC *proc, TransactionId latestXid);
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externvoidProcArrayEndTransaction(PGPROC*proc,TransactionIdlatestXid);
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externvoidProcArrayClearTransaction(PGPROC*proc);
2828

29+
externvoidProcArrayInitRecovery(TransactionIdinitializedUptoXID);
2930
externvoidProcArrayApplyRecoveryInfo(RunningTransactionsrunning);
3031
externvoidProcArrayApplyXidAssignment(TransactionIdtopxid,
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intnsubxids,TransactionId*subxids);

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