I don't like last minute patches before the final freeze, but I believe that

this one could be useful for people experiencing out-of-memory crashes while
executing queries which retrieve or use a very large number of tuples.

The problem happens when storage is allocated for functions results used in
a large query, for example:

  select upper(name) from big_table;
  select big_table.array[1] from big_table;
  select count(upper(name)) from big_table;

This patch is a dirty hack that fixes the out-of-memory problem for the most
common cases, like the above ones. It is not the final solution for the
problem but it can work for some people, so I'm posting it.

The patch should be safe because all changes are under #ifdef. Furthermore
the feature can be enabled or disabled at runtime by the `free_tuple_memory'
options in the pg_options file. The option is disabled by default and must
be explicitly enabled at runtime to have any effect.

To enable the patch add the follwing line to Makefile.custom:

CUSTOM_COPT += -DFREE_TUPLE_MEMORY

To enable the option at runtime add the following line to pg_option:

free_tuple_memory=1

Massimo

src/backend/access/common/heaptuple.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/access/common/heaptuple.c,v 1.51 1999/05/25 16:06:35 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/access/common/heaptuple.c,v 1.52 1999/06/12 14:05:36 momjian Exp $
  *
  * NOTES
  *	  The old interface functions have been converted to macros
@@ -27,6 +27,11 @@
 #include <storage/bufpage.h>
 #include <utils/memutils.h>
 
+#ifdef FREE_TUPLE_MEMORY
+#include <utils/portal.h>
+#include <utils/trace.h>
+#endif
+
 #ifndef HAVE_MEMMOVE
 #include <regex/utils.h>
 #else
@@ -93,6 +98,9 @@ DataFill(char *data,
 	int			i;
 	int			numberOfAttributes = tupleDesc->natts;
 	Form_pg_attribute *att = tupleDesc->attrs;
+#ifdef FREE_TUPLE_MEMORY
+	bool		free_tuple_memory = pg_options[OPT_FREE_TUPLE_MEMORY];
+#endif
 
 	if (bit != NULL)
 	{
@@ -131,6 +139,14 @@ DataFill(char *data,
 				*infomask |= HEAP_HASVARLENA;
 				data_length = VARSIZE(DatumGetPointer(value[i]));
 				memmove(data, DatumGetPointer(value[i]), data_length);
+#ifdef FREE_TUPLE_MEMORY
+				/* try to pfree value[i] - dz */
+				if (free_tuple_memory &&
+					PortalHeapMemoryIsValid(CurrentMemoryContext,
+											(Pointer) value[i])) {
+					pfree(value[i]);
+				}
+#endif
 				break;
 			case sizeof(char):
 				*data = att[i]->attbyval ?
@@ -147,8 +163,15 @@ DataFill(char *data,
 								   *((int32 *) value[i]));
 				break;
 			default:
-				memmove(data, DatumGetPointer(value[i]),
-						att[i]->attlen);
+				memmove(data, DatumGetPointer(value[i]), att[i]->attlen);
+#ifdef FREE_TUPLE_MEMORY
+				/* try to pfree value[i] - dz */
+				if (free_tuple_memory &&
+					PortalHeapMemoryIsValid(CurrentMemoryContext,
+											(Pointer) value[i])) {
+					pfree(value[i]);
+				}
+#endif
 				break;
 		}
 		data = (char *) att_addlength((long) data, att[i]->attlen, value[i]);

src/backend/executor/nodeAgg.c

@@ -31,6 +31,11 @@
 #include "utils/syscache.h"
 #include "optimizer/clauses.h"
 
+#ifdef FREE_TUPLE_MEMORY
+#include <utils/portal.h>
+#include <utils/trace.h>
+#endif
+
 /*
  * AggFuncInfo -
  *	  keeps the transition functions information around
@@ -113,7 +118,9 @@ ExecAgg(Agg *node)
 				isNull1 = FALSE,
 				isNull2 = FALSE;
 	bool		qual_result;
-
+#ifdef FREE_TUPLE_MEMORY
+	bool		free_tuple_memory = pg_options[OPT_FREE_TUPLE_MEMORY];
+#endif
 
 	/* ---------------------
 	 *	get state info from node
@@ -241,6 +248,10 @@ ExecAgg(Agg *node)
 		for (;;)
 		{
 			TupleTableSlot *outerslot;
+#ifdef FREE_TUPLE_MEMORY
+			Oid				valueType;
+			bool			isByValue = 0;
+#endif
 
 			isNull = isNull1 = isNull2 = 0;
 			outerslot = ExecProcNode(outerPlan, (Plan *) node);
@@ -293,6 +304,31 @@ ExecAgg(Agg *node)
 					newVal = ExecEvalExpr(aggref->target, econtext,
 										  &isNull, &isDone);
 				}
+#ifdef FREE_TUPLE_MEMORY
+				if (free_tuple_memory) {
+					switch (nodeTag(aggref->target)) {
+					case T_Const:
+						isByValue = ((Const*) (aggref->target))->constbyval;
+						break;
+					case T_Var:
+						valueType = ((Var*) (aggref->target))->vartype;
+						isByValue = typeByVal(typeidType(valueType));
+						break;
+					case T_Array:
+						isByValue = ((Array*)(aggref->target))->arrayelembyval;
+						break;
+					case T_ArrayRef:
+						isByValue =((ArrayRef*)(aggref->target))->refelembyval;
+						break;
+					case T_Expr:
+						valueType = ((Expr*) (aggref->target))->typeOid;
+						isByValue = typeByVal(typeidType(valueType));
+						break;
+					default:
+						break;
+					}
+				}
+#endif
 
 				if (isNull && !aggref->usenulls)
 					continue;	/* ignore this tuple for this agg */
@@ -353,6 +389,16 @@ ExecAgg(Agg *node)
 										  (FmgrValues *) args, &isNull2);
 					Assert(!isNull2);
 				}
+
+#ifdef FREE_TUPLE_MEMORY
+				/* try to pfree newVal if not isByValue - dz */
+				if (free_tuple_memory && !isByValue && 
+					PortalHeapMemoryIsValid(CurrentMemoryContext,
+											(Pointer) newVal))
+				{
+					pfree(newVal);
+				}
+#endif
 			}
 
 			/*

src/backend/utils/misc/trace.c

@@ -73,6 +73,9 @@ static char *opt_names[] = {
 	"syslog",					/* use syslog for error messages */
 	"hostlookup",				/* enable hostname lookup in ps_status */
 	"showportnumber",			/* show port number in ps_status */
+#ifdef FREE_TUPLE_MEMORY
+	"free_tuple_memory",		/* try to pfree memory for each tuple */
+#endif
 
 	/* NUM_PG_OPTIONS */		/* must be the last item of enum */
 };
@@ -404,9 +407,9 @@ read_pg_options(SIGNAL_ARGS)
 }
 
 /*
- * Local variables:
- *	tab-width: 4
- *	c-indent-level: 4
- *	c-basic-offset: 4
+ * Local Variables:
+ *  tab-width: 4
+ *  c-indent-level: 4
+ *  c-basic-offset: 4
  * End:
  */

src/backend/utils/mmgr/portalmem.c

@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/utils/mmgr/portalmem.c,v 1.19 1999/05/25 16:12:55 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/utils/mmgr/portalmem.c,v 1.20 1999/06/12 14:05:39 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -289,6 +289,24 @@ PortalHeapMemoryFree(PortalHeapMemory this,
 	}
 }
 
+#ifdef FREE_TUPLE_MEMORY
+/*
+ * PortalHeapMemoryIsValid --
+ *
+ * Check if a pointer is allocated in a memory context.
+ *
+ */
+bool
+PortalHeapMemoryIsValid(MemoryContext context, Pointer pointer)
+{
+	HeapMemoryBlock block = HEAPMEMBLOCK((PortalHeapMemory) context);
+
+	AssertState(PointerIsValid(block));
+
+	return (AllocSetContains(&block->setData, pointer));
+}
+#endif
+
 /* ----------------
  *		PortalHeapMemoryRealloc
  * ----------------

src/include/utils/portal.h

@@ -6,7 +6,7 @@
  *
  * Copyright (c) 1994, Regents of the University of California
  *
- * $Id: portal.h,v 1.13 1999/05/25 16:14:57 momjian Exp $
+ * $Id: portal.h,v 1.14 1999/06/12 14:05:40 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -80,6 +80,10 @@ extern void EndPortalAllocMode(void);
 extern PortalVariableMemory PortalGetVariableMemory(Portal portal);
 extern PortalHeapMemory PortalGetHeapMemory(Portal portal);
 
+#ifdef FREE_TUPLE_MEMORY
+bool   PortalHeapMemoryIsValid(MemoryContext context, Pointer pointer);
+#endif
+
 /* estimate of the maximum number of open portals a user would have,
  * used in initially sizing the PortalHashTable in	EnablePortalManager()
  */

src/include/utils/trace.h

@@ -64,6 +64,9 @@ enum pg_option_enum {
 	OPT_SYSLOG,					/* use syslog for error messages */
 	OPT_HOSTLOOKUP,				/* enable hostname lookup in ps_status */
 	OPT_SHOWPORTNUMBER,			/* show port number in ps_status */
+#ifdef FREE_TUPLE_MEMORY
+	OPT_FREE_TUPLE_MEMORY,		/* try to pfree memory for each tuple */
+#endif
 
 	NUM_PG_OPTIONS				/* must be the last item of enum */
 };
@@ -83,9 +86,9 @@ extern int	pg_options[NUM_PG_OPTIONS];
 #endif	 /* TRACE_H */
 
 /*
- * Local variables:
- *	tab-width: 4
- *	c-indent-level: 4
- *	c-basic-offset: 4
+ * Local Variables:
+ *  tab-width: 4
+ *  c-indent-level: 4
+ *  c-basic-offset: 4
  * End:
  */