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 8a5888a40447edc26b76aeaf38464abbbd3216df..7ed53be85d43632aeb9e34aee8b218ae6c04ead6 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 1.198 2006/01/05 10:07:45 petere Exp $
+ *       $PostgreSQL: pgsql/src/backend/commands/trigger.c,v 1.199 2006/01/12 21:48:52 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1736,7 +1736,8 @@ 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 1f70b2704adf1b2071e0e611bb8e5faa42f72873..a0f9cfedd3f17d7f042e73382d3c01f886ba8d34 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 1.264 2006/01/11 08:43:12 neilc Exp $
+ *       $PostgreSQL: pgsql/src/backend/executor/execMain.c,v 1.265 2006/01/12 21:48:53 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1213,7 +1213,8 @@ lnext:    ;
                                                                newSlot = EvalPlanQual(estate,
                                                                                                           erm->rti,
                                                                                                           &update_ctid,
-                                                                                                          update_xmax);
+                                                                                                          update_xmax,
+                                                                                                          estate->es_snapshot->curcid);
                                                                if (!TupIsNull(newSlot))
                                                                {
                                                                        slot = newSlot;
@@ -1521,7 +1522,8 @@ ldelete:;
                                epqslot = EvalPlanQual(estate,
                                                                           resultRelInfo->ri_RangeTableIndex,
                                                                           &update_ctid,
-                                                                          update_xmax);
+                                                                          update_xmax,
+                                                                          estate->es_snapshot->curcid);
                                if (!TupIsNull(epqslot))
                                {
                                        *tupleid = update_ctid;
@@ -1673,7 +1675,8 @@ lreplace:;
                                epqslot = EvalPlanQual(estate,
                                                                           resultRelInfo->ri_RangeTableIndex,
                                                                           &update_ctid,
-                                                                          update_xmax);
+                                                                          update_xmax,
+                                                                          estate->es_snapshot->curcid);
                                if (!TupIsNull(epqslot))
                                {
                                        *tupleid = update_ctid;
@@ -1820,6 +1823,7 @@ 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)
@@ -1829,7 +1833,7 @@ ExecConstraints(ResultRelInfo *resultRelInfo,
  */
 TupleTableSlot *
 EvalPlanQual(EState *estate, Index rti,
-                        ItemPointer tid, TransactionId priorXmax)
+                        ItemPointer tid, TransactionId priorXmax, CommandId curCid)
 {
        evalPlanQual *epq;
        EState     *epqstate;
@@ -1905,6 +1909,24 @@ 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 facb10a2e25929420b9af75cf775455665fbf3b7..e320a8bf92641cfe74e101793f2bd5d8b8508188 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 1.123 2005/12/03 05:51:03 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/executor/executor.h,v 1.124 2006/01/12 21:48:53 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