Fix potential failure when hashing the output of a subplan that produces

a pass-by-reference datatype with a nontrivial projection step.
We were using the same memory context for the projection operation as for
the temporary context used by the hashtable routines in execGrouping.c.
However, the hashtable routines feel free to reset their temp context at
any time, which'd lead to destroying input data that was still needed.
Report and diagnosis by Tao Ma.

Back-patch to 8.1, where the problem was introduced by the changes that
allowed us to work with "virtual" tuples instead of materializing intermediate
tuple values everywhere.  The earlier code looks quite similar, but it doesn't
suffer the problem because the data gets copied into another context as a
result of having to materialize ExecProject's output tuple.

diff --git a/src/backend/executor/nodeSubplan.c b/src/backend/executor/nodeSubplan.c
index f5ac47402e13984189679bba9fabe1d867b0733e..d397b136fd326c1be4a720361a5a08b3517dffb8 100644 (file)
--- a/src/backend/executor/nodeSubplan.c
+++ b/src/backend/executor/nodeSubplan.c
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *       $PostgreSQL: pgsql/src/backend/executor/nodeSubplan.c,v 1.101 2010/01/02 16:57:45 momjian Exp $
+ *       $PostgreSQL: pgsql/src/backend/executor/nodeSubplan.c,v 1.101.6.1 2010/07/28 04:50:58 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -89,7 +89,6 @@ ExecHashSubPlan(SubPlanState *node,
 {
        SubPlan    *subplan = (SubPlan *) node->xprstate.expr;
        PlanState  *planstate = node->planstate;
-       ExprContext *innerecontext = node->innerecontext;
        TupleTableSlot *slot;
 
        /* Shouldn't have any direct correlation Vars */
@@ -126,12 +125,6 @@ ExecHashSubPlan(SubPlanState *node,
         * it still needs to free the tuple.
         */
 
-       /*
-        * Since the hashtable routines will use innerecontext's per-tuple memory
-        * as working memory, be sure to reset it for each tuple.
-        */
-       ResetExprContext(innerecontext);
-
        /*
         * If the LHS is all non-null, probe for an exact match in the main hash
         * table.  If we find one, the result is TRUE. Otherwise, scan the
@@ -438,7 +431,6 @@ buildSubPlanHash(SubPlanState *node, ExprContext *econtext)
        PlanState  *planstate = node->planstate;
        int                     ncols = list_length(subplan->paramIds);
        ExprContext *innerecontext = node->innerecontext;
-       MemoryContext tempcxt = innerecontext->ecxt_per_tuple_memory;
        MemoryContext oldcontext;
        int                     nbuckets;
        TupleTableSlot *slot;
@@ -460,7 +452,7 @@ buildSubPlanHash(SubPlanState *node, ExprContext *econtext)
         * If it's not necessary to distinguish FALSE and UNKNOWN, then we don't
         * need to store subplan output rows that contain NULL.
         */
-       MemoryContextReset(node->tablecxt);
+       MemoryContextReset(node->hashtablecxt);
        node->hashtable = NULL;
        node->hashnulls = NULL;
        node->havehashrows = false;
@@ -476,8 +468,8 @@ buildSubPlanHash(SubPlanState *node, ExprContext *econtext)
                                                                                  node->tab_hash_funcs,
                                                                                  nbuckets,
                                                                                  sizeof(TupleHashEntryData),
-                                                                                 node->tablecxt,
-                                                                                 tempcxt);
+                                                                                 node->hashtablecxt,
+                                                                                 node->hashtempcxt);
 
        if (!subplan->unknownEqFalse)
        {
@@ -495,8 +487,8 @@ buildSubPlanHash(SubPlanState *node, ExprContext *econtext)
                                                                                          node->tab_hash_funcs,
                                                                                          nbuckets,
                                                                                          sizeof(TupleHashEntryData),
-                                                                                         node->tablecxt,
-                                                                                         tempcxt);
+                                                                                         node->hashtablecxt,
+                                                                                         node->hashtempcxt);
        }
 
        /*
@@ -555,7 +547,7 @@ buildSubPlanHash(SubPlanState *node, ExprContext *econtext)
 
                /*
                 * Reset innerecontext after each inner tuple to free any memory used
-                * in hash computation or comparison routines.
+                * during ExecProject.
                 */
                ResetExprContext(innerecontext);
        }
@@ -680,7 +672,8 @@ ExecInitSubPlan(SubPlan *subplan, PlanState *parent)
        sstate->projRight = NULL;
        sstate->hashtable = NULL;
        sstate->hashnulls = NULL;
-       sstate->tablecxt = NULL;
+       sstate->hashtablecxt = NULL;
+       sstate->hashtempcxt = NULL;
        sstate->innerecontext = NULL;
        sstate->keyColIdx = NULL;
        sstate->tab_hash_funcs = NULL;
@@ -730,12 +723,19 @@ ExecInitSubPlan(SubPlan *subplan, PlanState *parent)
                ListCell   *l;
 
                /* We need a memory context to hold the hash table(s) */
-               sstate->tablecxt =
+               sstate->hashtablecxt =
                        AllocSetContextCreate(CurrentMemoryContext,
                                                                  "Subplan HashTable Context",
                                                                  ALLOCSET_DEFAULT_MINSIZE,
                                                                  ALLOCSET_DEFAULT_INITSIZE,
                                                                  ALLOCSET_DEFAULT_MAXSIZE);
+               /* and a small one for the hash tables to use as temp storage */
+               sstate->hashtempcxt =
+                       AllocSetContextCreate(CurrentMemoryContext,
+                                                                 "Subplan HashTable Temp Context",
+                                                                 ALLOCSET_SMALL_MINSIZE,
+                                                                 ALLOCSET_SMALL_INITSIZE,
+                                                                 ALLOCSET_SMALL_MAXSIZE);
                /* and a short-lived exprcontext for function evaluation */
                sstate->innerecontext = CreateExprContext(estate);
                /* Silly little array of column numbers 1..n */

diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index 6455eeaa603a64a06c0677010b298824ff1ce60e..928cf4c5a555591cd6fc84ca8b8d3e8d61a9dd4c 100644 (file)
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/nodes/execnodes.h,v 1.219 2010/02/26 02:01:25 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/nodes/execnodes.h,v 1.219.4.1 2010/07/28 04:50:58 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -699,8 +699,9 @@ typedef struct SubPlanState
        TupleHashTable hashnulls;       /* hash table for rows with null(s) */
        bool            havehashrows;   /* TRUE if hashtable is not empty */
        bool            havenullrows;   /* TRUE if hashnulls is not empty */
-       MemoryContext tablecxt;         /* memory context containing tables */
-       ExprContext *innerecontext; /* working context for comparisons */
+       MemoryContext hashtablecxt;     /* memory context containing hash tables */
+       MemoryContext hashtempcxt;      /* temp memory context for hash tables */
+       ExprContext *innerecontext; /* econtext for computing inner tuples */
        AttrNumber *keyColIdx;          /* control data for hash tables */
        FmgrInfo   *tab_hash_funcs; /* hash functions for table datatype(s) */
        FmgrInfo   *tab_eq_funcs;       /* equality functions for table datatype(s) */

diff --git a/src/test/regress/expected/subselect.out b/src/test/regress/expected/subselect.out
index e839ad7f9647b1ffc9141a1bc71a1936089bb84d..7f8c05bc800c57d60661a9fb21503cde49101347 100644 (file)
--- a/src/test/regress/expected/subselect.out
+++ b/src/test/regress/expected/subselect.out
@@ -521,3 +521,12 @@ from
 -----
 (0 rows)
 
+--
+-- Test case for premature memory release during hashing of subplan output
+--
+select '1'::text in (select '1'::name union all select '1'::name);
+ ?column? 
+----------
+ t
+(1 row)
+

diff --git a/src/test/regress/sql/subselect.sql b/src/test/regress/sql/subselect.sql
index f6657fa535c50d635326f1f576284a3d69930a06..9d13c39c8ab7f6baedc3bf545786888f4bf2b6e8 100644 (file)
--- a/src/test/regress/sql/subselect.sql
+++ b/src/test/regress/sql/subselect.sql
@@ -335,3 +335,9 @@ from
    from int8_tbl) sq0
   join
   int4_tbl i4 on dummy = i4.f1;
+
+--
+-- Test case for premature memory release during hashing of subplan output
+--
+
+select '1'::text in (select '1'::name union all select '1'::name);