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.

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 1.102 2010/07/12 17:01:05 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/nodeSubplan.c,v 1.103 2010/07/28 04:50:50 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 */

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 1.220 2010/07/28 04:50:50 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) */

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)
+

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);