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Commit060bb38

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Ignore nextOid when replaying an ONLINE checkpoint.
The nextOid value is from the start of the checkpoint and may well be stalecompared to values from more recent XLOG_NEXTOID records. Previously, weadopted it anyway, allowing the OID counter to go backwards during a crash.While this should be harmless, it contributed to the severity of the bugfixed in commit0408e1e, by allowing duplicate TOAST OIDs to be assignedimmediately following a crash. Without this error, that issue would onlyhave arisen when TOAST objects just younger than a multiple of 2^32 OIDswere deleted and then not vacuumed in time to avoid a conflict.Pavan DeolaseeDiscussion:https://postgr.es/m/CABOikdOgWT2hHkYG3Wwo2cyZJq2zfs1FH0FgX-=h4OLosXHf9w@mail.gmail.com
1 parent8bba10f commit060bb38

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  • src/backend/access/transam

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+14
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‎src/backend/access/transam/xlog.c

Lines changed: 14 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -9420,11 +9420,20 @@ xlog_redo(XLogReaderState *record)
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checkPoint.nextXid))
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ShmemVariableCache->nextXid=checkPoint.nextXid;
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LWLockRelease(XidGenLock);
9423-
/* ... but still treat OID counter as exact */
9424-
LWLockAcquire(OidGenLock,LW_EXCLUSIVE);
9425-
ShmemVariableCache->nextOid=checkPoint.nextOid;
9426-
ShmemVariableCache->oidCount=0;
9427-
LWLockRelease(OidGenLock);
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/*
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* We ignore the nextOid counter in an ONLINE checkpoint, preferring
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* to track OID assignment through XLOG_NEXTOID records. The nextOid
9427+
* counter is from the start of the checkpoint and might well be stale
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* compared to later XLOG_NEXTOID records. We could try to take the
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* maximum of the nextOid counter and our latest value, but since
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* there's no particular guarantee about the speed with which the OID
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* counter wraps around, that's a risky thing to do. In any case,
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* users of the nextOid counter are required to avoid assignment of
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* duplicates, so that a somewhat out-of-date value should be safe.
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*/
9435+
9436+
/* Handle multixact */
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MultiXactAdvanceNextMXact(checkPoint.nextMulti,
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checkPoint.nextMultiOffset);
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