From e76bb5cfec543cbf9243f66bf020da9058c22aa4 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Thu, 12 Jan 2006 21:49:32 +0000 Subject: [PATCH] Repair "Halloween problem" in EvalPlanQual: a tuple that's been inserted by our own command (or more generally, xmin = our xact and cmin >= current command ID) should not be seen as good. Else we may try to update rows we already updated. This error was inserted last August while fixing the even bigger problem that the old coding wouldn't see *any* tuples inserted by our own transaction as good. Per report from Euler Taveira de Oliveira. --- src/backend/commands/trigger.c | 5 +++-- src/backend/executor/execMain.c | 32 +++++++++++++++++++++++++++----- src/include/executor/executor.h | 4 ++-- 3 files changed, 32 insertions(+), 9 deletions(-) diff --git a/src/backend/commands/trigger.c b/src/backend/commands/trigger.c index f49fa1a02fd..4b9d5efea98 100644 --- a/src/backend/commands/trigger.c +++ b/src/backend/commands/trigger.c @@ -7,7 +7,7 @@ * Portions Copyright (c) 1994, Regents of the University of California * * IDENTIFICATION - * $Header: /cvsroot/pgsql/src/backend/commands/trigger.c,v 1.159.2.1 2005/08/25 22:07:15 tgl Exp $ + * $Header: /cvsroot/pgsql/src/backend/commands/trigger.c,v 1.159.2.2 2006/01/12 21:49:31 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -1592,7 +1592,8 @@ ltrmark:; epqslot = EvalPlanQual(estate, relinfo->ri_RangeTableIndex, &update_ctid, - update_xmax); + update_xmax, + cid); if (!TupIsNull(epqslot)) { *tid = update_ctid; diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c index c3c2d83d808..ac952ca6238 100644 --- a/src/backend/executor/execMain.c +++ b/src/backend/executor/execMain.c @@ -26,7 +26,7 @@ * * * IDENTIFICATION - * $Header: /cvsroot/pgsql/src/backend/executor/execMain.c,v 1.220.2.3 2005/08/25 22:07:18 tgl Exp $ + * $Header: /cvsroot/pgsql/src/backend/executor/execMain.c,v 1.220.2.4 2006/01/12 21:49:32 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -1202,7 +1202,8 @@ lnext: ; newSlot = EvalPlanQual(estate, erm->rti, &update_ctid, - update_xmax); + update_xmax, + estate->es_snapshot->curcid); if (!TupIsNull(newSlot)) { slot = newSlot; @@ -1508,7 +1509,8 @@ ldelete:; epqslot = EvalPlanQual(estate, resultRelInfo->ri_RangeTableIndex, &update_ctid, - update_xmax); + update_xmax, + estate->es_snapshot->curcid); if (!TupIsNull(epqslot)) { *tupleid = update_ctid; @@ -1648,7 +1650,8 @@ lreplace:; epqslot = EvalPlanQual(estate, resultRelInfo->ri_RangeTableIndex, &update_ctid, - update_xmax); + update_xmax, + estate->es_snapshot->curcid); if (!TupIsNull(epqslot)) { *tupleid = update_ctid; @@ -1802,6 +1805,7 @@ ExecConstraints(ResultRelInfo *resultRelInfo, * rti - rangetable index of table containing tuple * *tid - t_ctid from the outdated tuple (ie, next updated version) * priorXmax - t_xmax from the outdated tuple + * curCid - command ID of current command of my transaction * * *tid is also an output parameter: it's modified to hold the TID of the * latest version of the tuple (note this may be changed even on failure) @@ -1811,7 +1815,7 @@ ExecConstraints(ResultRelInfo *resultRelInfo, */ TupleTableSlot * EvalPlanQual(EState *estate, Index rti, - ItemPointer tid, TransactionId priorXmax) + ItemPointer tid, TransactionId priorXmax, CommandId curCid) { evalPlanQual *epq; EState *epqstate; @@ -1887,6 +1891,24 @@ EvalPlanQual(EState *estate, Index rti, continue; /* loop back to repeat heap_fetch */ } + /* + * If tuple was inserted by our own transaction, we have to check + * cmin against curCid: cmin >= curCid means our command cannot + * see the tuple, so we should ignore it. Without this we are + * open to the "Halloween problem" of indefinitely re-updating + * the same tuple. (We need not check cmax because + * HeapTupleSatisfiesDirty will consider a tuple deleted by + * our transaction dead, regardless of cmax.) We just checked + * that priorXmax == xmin, so we can test that variable instead + * of doing HeapTupleHeaderGetXmin again. + */ + if (TransactionIdIsCurrentTransactionId(priorXmax) && + HeapTupleHeaderGetCmin(tuple.t_data) >= curCid) + { + ReleaseBuffer(buffer); + return NULL; + } + /* * We got tuple - now copy it for use by recheck query. */ diff --git a/src/include/executor/executor.h b/src/include/executor/executor.h index 29a50a7f590..afa9798426a 100644 --- a/src/include/executor/executor.h +++ b/src/include/executor/executor.h @@ -7,7 +7,7 @@ * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * - * $Id: executor.h,v 1.102.2.4 2005/08/25 22:07:21 tgl Exp $ + * $Id: executor.h,v 1.102.2.5 2006/01/12 21:49:32 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -98,7 +98,7 @@ extern bool ExecContextForcesOids(PlanState *planstate, bool *hasoids); extern void ExecConstraints(ResultRelInfo *resultRelInfo, TupleTableSlot *slot, EState *estate); extern TupleTableSlot *EvalPlanQual(EState *estate, Index rti, - ItemPointer tid, TransactionId priorXmax); + ItemPointer tid, TransactionId priorXmax, CommandId curCid); /* * prototypes from functions in execProcnode.c