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Commit8f4fe8d

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Reset properly snapshot export state during transaction abort
During a replication slot creation, an ERROR generated in the sametransaction as the one creating a to-be-exported snapshot would haveleft the backend in an inconsistent state, as the associated staticexport snapshot state was not being reset on transaction abort, but onlyon the follow-up command received by the WAL sender that created thissnapshot on replication slot creation. This would trigger inconsistencyfailures if this session tried to export again a snapshot, like duringthe creation of a replication slot.Note that a snapshot export cannot happen in a transaction block, sothere is no need to worry resetting this state for subtransactionaborts. Also, this inconsistent state would very unlikely show up tousers. For example, one case where this could happen is anout-of-memory error when building the initial snapshot to-be-exported.Dilip found this problem while poking at a different patch, that causedan error in this code path for reasons unrelated to HEAD.Author: Dilip KumarReviewed-by: Michael Paquier, Zhihong YuDiscussion:https://postgr.es/m/CAFiTN-s0zA1Kj0ozGHwkYkHwa5U0zUE94RSc_g81WrpcETB5=w@mail.gmail.comBackpatch-through: 9.6
1 parent0b5f557 commit8f4fe8d

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3 files changed

+28
-2
lines changed

3 files changed

+28
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lines changed

‎src/backend/access/transam/xact.c

Lines changed: 9 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -46,6 +46,7 @@
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#include"replication/logical.h"
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#include"replication/logicallauncher.h"
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#include"replication/origin.h"
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#include"replication/snapbuild.h"
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#include"replication/syncrep.h"
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#include"replication/walsender.h"
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#include"storage/condition_variable.h"
@@ -2677,6 +2678,9 @@ AbortTransaction(void)
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/* Forget about any active REINDEX. */
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ResetReindexState(s->nestingLevel);
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/* Reset snapshot export state. */
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SnapBuildResetExportedSnapshotState();
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/* If in parallel mode, clean up workers and exit parallel mode. */
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if (IsInParallelMode())
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{
@@ -4987,6 +4991,11 @@ AbortSubTransaction(void)
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/* Forget about any active REINDEX. */
49884992
ResetReindexState(s->nestingLevel);
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/*
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* No need for SnapBuildResetExportedSnapshotState() here, snapshot
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* exports are not supported in subtransactions.
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*/
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/* Exit from parallel mode, if necessary. */
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if (IsInParallelMode())
49925001
{

‎src/backend/replication/logical/snapbuild.c

Lines changed: 18 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -691,17 +691,33 @@ SnapBuildGetOrBuildSnapshot(SnapBuild *builder, TransactionId xid)
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void
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SnapBuildClearExportedSnapshot(void)
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{
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ResourceOwnertmpResOwner;
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/* nothing exported, that is the usual case */
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if (!ExportInProgress)
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return;
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698700
if (!IsTransactionState())
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elog(ERROR,"clearing exported snapshot in wrong transaction state");
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701-
/* make sure nothing could have ever happened */
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/*
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* AbortCurrentTransaction() takes care of resetting the snapshot state,
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* so remember SavedResourceOwnerDuringExport.
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*/
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tmpResOwner=SavedResourceOwnerDuringExport;
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/* make sure nothing could have ever happened */
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AbortCurrentTransaction();
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CurrentResourceOwner=SavedResourceOwnerDuringExport;
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CurrentResourceOwner=tmpResOwner;
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}
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/*
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* Clear snapshot export state during transaction abort.
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*/
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void
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SnapBuildResetExportedSnapshotState(void)
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{
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SavedResourceOwnerDuringExport=NULL;
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ExportInProgress= false;
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}

‎src/include/replication/snapbuild.h

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Original file line numberDiff line numberDiff line change
@@ -69,6 +69,7 @@ extern void SnapBuildSnapDecRefcount(Snapshot snap);
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externSnapshotSnapBuildInitialSnapshot(SnapBuild*builder);
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externconstchar*SnapBuildExportSnapshot(SnapBuild*snapstate);
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externvoidSnapBuildClearExportedSnapshot(void);
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externvoidSnapBuildResetExportedSnapshotState(void);
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externSnapBuildStateSnapBuildCurrentState(SnapBuild*snapstate);
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externSnapshotSnapBuildGetOrBuildSnapshot(SnapBuild*builder,

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