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.

diff --git a/src/backend/commands/trigger.c b/src/backend/commands/trigger.c
index ec998aa7b9f76ab6679b9de85f7bc79af9f073e4..a6b75f06d58265eaccf2cd405d705de88c370362 100644 (file)
--- 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
- *       $PostgreSQL: pgsql/src/backend/commands/trigger.c,v 1.177.4.2 2005/08/25 19:44:57 tgl Exp $
+ *       $PostgreSQL: pgsql/src/backend/commands/trigger.c,v 1.177.4.3 2006/01/12 21:49:16 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1603,7 +1603,8 @@ 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 a825c2816185e5fa5828e4cbae11f9c99b2373c8..3a86d31162969d83c2809beaec027753e91ab9f8 100644 (file)
--- a/src/backend/executor/execMain.c
+++ b/src/backend/executor/execMain.c
@@ -26,7 +26,7 @@
  *
  *
  * IDENTIFICATION
- *       $PostgreSQL: pgsql/src/backend/executor/execMain.c,v 1.241.4.1 2005/08/25 19:45:00 tgl Exp $
+ *       $PostgreSQL: pgsql/src/backend/executor/execMain.c,v 1.241.4.2 2006/01/12 21:49:17 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1159,7 +1159,8 @@ lnext:    ;
                                                                newSlot = EvalPlanQual(estate,
                                                                                                           erm->rti,
                                                                                                           &update_ctid,
-                                                                                                          update_xmax);
+                                                                                                          update_xmax,
+                                                                                                          estate->es_snapshot->curcid);
                                                                if (!TupIsNull(newSlot))
                                                                {
                                                                        slot = newSlot;
@@ -1470,7 +1471,8 @@ ldelete:;
                                epqslot = EvalPlanQual(estate,
                                                                           resultRelInfo->ri_RangeTableIndex,
                                                                           &update_ctid,
-                                                                          update_xmax);
+                                                                          update_xmax,
+                                                                          estate->es_snapshot->curcid);
                                if (!TupIsNull(epqslot))
                                {
                                        *tupleid = update_ctid;
@@ -1615,7 +1617,8 @@ lreplace:;
                                epqslot = EvalPlanQual(estate,
                                                                           resultRelInfo->ri_RangeTableIndex,
                                                                           &update_ctid,
-                                                                          update_xmax);
+                                                                          update_xmax,
+                                                                          estate->es_snapshot->curcid);
                                if (!TupIsNull(epqslot))
                                {
                                        *tupleid = update_ctid;
@@ -1770,6 +1773,7 @@ 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)
@@ -1779,7 +1783,7 @@ ExecConstraints(ResultRelInfo *resultRelInfo,
  */
 TupleTableSlot *
 EvalPlanQual(EState *estate, Index rti,
-                        ItemPointer tid, TransactionId priorXmax)
+                        ItemPointer tid, TransactionId priorXmax, CommandId curCid)
 {
        evalPlanQual *epq;
        EState     *epqstate;
@@ -1855,6 +1859,24 @@ 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 6c7eff0d46dabf1217ac93c549e67f18b0235a0f..77f7310d5ea36a139c2127ac6457413cb52050f7 100644 (file)
--- a/src/include/executor/executor.h
+++ b/src/include/executor/executor.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/executor/executor.h,v 1.115.4.1 2005/08/25 19:45:06 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/executor/executor.h,v 1.115.4.2 2006/01/12 21:49:19 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -109,7 +109,7 @@ 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