Theses buffer leaks are caused by indexes that are kept open between

calls. Outside a transaction, the backend detects them as buffer
leaks; it sends a NOTICE, and frees them. This sometimes cause a
segmentation fault (at least on Linux). These indexes are initialized
on the first lo_read/lo_write/lo_tell call, and (normally) closed
on a lo_close call.  Thus the buffer leaks appear when lo direct
access functions are used, and not with lo_import/lo_export functions
(libpq version calls lo_close before ending the command, and the
backend version uses another path).

The included patches (against recent snapshot, and against 6.3.2)
cause indexes to be closed on transaction end (that is on explicit
'END' statment, or on command termination outside trasaction blocks),
thus preventing the buffer leaks while increasing performance inside
transactions. Some (all?) 'classic' memory leaks are also removed.

I hope it will be ok.

--- Pascal ANDRE, graduated from Ecole Centrale Paris andre@via.ecp.fr

Author: bmomjian

src/backend/access/transam/xact.c

@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/access/transam/xact.c,v 1.20 1998/06/15 19:28:02 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/access/transam/xact.c,v 1.21 1998/07/21 04:17:21 momjian Exp $
  *
  * NOTES
  *		Transaction aborts can now occur two ways:
@@ -137,6 +137,11 @@
  *-------------------------------------------------------------------------
  */
 
+/*
+ * Large object clean up added in CommitTransaction() to prevent buffer leaks.
+ * [PA, 7/17/98]
+ * [PA] is Pascal André <andre@via.ecp.fr>
+ */
 #include <postgres.h>
 
 #include <access/xact.h>
@@ -151,6 +156,9 @@
 #include <commands/async.h>
 #include <commands/sequence.h>
 
+/* included for _lo_commit [PA, 7/17/98] */
+#include <libpq/be-fsstubs.h>
+
 static void AbortTransaction(void);
 static void AtAbort_Cache(void);
 static void AtAbort_Locks(void);
@@ -889,6 +897,10 @@ CommitTransaction()
 	 *	do commit processing
 	 * ----------------
 	 */
+
+	/* handle commit for large objects [ PA, 7/17/98 ] */ 
+	_lo_commit();
+
 	CloseSequences();
 	DestroyTempRels();
 	AtEOXact_portals();

src/backend/libpq/be-fsstubs.c

@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/libpq/be-fsstubs.c,v 1.21 1998/06/15 19:28:25 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/libpq/be-fsstubs.c,v 1.22 1998/07/21 04:17:23 momjian Exp $
  *
  * NOTES
  *	  This should be moved to a more appropriate place.  It is here
@@ -41,6 +41,8 @@
 #include <storage/large_object.h>
 #include <libpq/be-fsstubs.h>
 
+/* [PA] is Pascal André <andre@via.ecp.fr> */
+
 /*#define FSDB 1*/
 #define MAX_LOBJ_FDS 256
 
@@ -52,7 +54,6 @@ static GlobalMemory fscxt = NULL;
 static int	newLOfd(LargeObjectDesc *lobjCookie);
 static void deleteLOfd(int fd);
 
-
 /*****************************************************************************
  *	File Interfaces for Large Objects
  *****************************************************************************/
@@ -367,6 +368,26 @@ lo_export(Oid lobjId, text *filename)
 	return 1;
 }
 
+/*
+ * lo_commit -
+ *       prepares large objects for transaction commit [PA, 7/17/98]
+ */
+void 
+_lo_commit(void)
+{
+        int i;
+	MemoryContext currentContext;
+
+	currentContext = MemoryContextSwitchTo((MemoryContext) fscxt);
+
+        for (i = 0; i < MAX_LOBJ_FDS; i++) {
+                if (cookies[i] != NULL) inv_cleanindex(cookies[i]);
+        }
+
+	MemoryContextSwitchTo(currentContext);
+
+}
+
 
 /*****************************************************************************
  *	Support routines for this file

src/backend/storage/large_object/inv_api.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/storage/large_object/inv_api.c,v 1.30 1998/06/15 19:29:16 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/storage/large_object/inv_api.c,v 1.31 1998/07/21 04:17:24 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -60,6 +60,19 @@
  *	for data.
  */
 
+/*
+ *      In order to prevent buffer leak on transaction commit, large object
+ *      scan index handling has been modified. Indexes are persistant inside
+ *      a transaction but may be closed between two calls to this API (when 
+ *      transaction is committed while object is opened, or when no 
+ *      transaction is active). Scan indexes are thus now reinitialized using
+ *      the object current offset. [PA]
+ *
+ *      Some cleanup has been also done for non freed memory.
+ *
+ *      For subsequent notes, [PA] is Pascal André <andre@via.ecp.fr>
+ */
+
 #define IFREESPC(p)		(PageGetFreeSpace(p) - sizeof(HeapTupleData) - sizeof(struct varlena) - sizeof(int32))
 #define IMAXBLK			8092
 #define IMINBLK			512
@@ -261,8 +274,11 @@ inv_close(LargeObjectDesc *obj_desc)
 {
 	Assert(PointerIsValid(obj_desc));
 
-	if (obj_desc->iscan != (IndexScanDesc) NULL)
+	if (obj_desc->iscan != (IndexScanDesc) NULL) {
 		index_endscan(obj_desc->iscan);
+		pfree(obj_desc->iscan);
+		obj_desc->iscan = NULL;
+	}
 
 	heap_close(obj_desc->heap_r);
 	index_close(obj_desc->index_r);
@@ -546,6 +562,28 @@ inv_write(LargeObjectDesc *obj_desc, char *buf, int nbytes)
 	return (nwritten);
 }
 
+/*
+ * inv_cleanindex --
+ *       Clean opened indexes for large objects, and clears current result.
+ *       This is necessary on transaction commit in order to prevent buffer
+ *       leak. 
+ *       This function must be called for each opened large object.
+ *       [ PA, 7/17/98 ]
+ */
+void 
+inv_cleanindex(LargeObjectDesc *obj_desc)
+{
+        Assert(PointerIsValid(obj_desc));
+
+	if (obj_desc->iscan == (IndexScanDesc) NULL) return;
+
+	index_endscan(obj_desc->iscan);
+	pfree(obj_desc->iscan);
+	obj_desc->iscan = (IndexScanDesc) NULL;
+	
+	ItemPointerSetInvalid(&(obj_desc->htid));
+}
+
 /*
  *	inv_fetchtup -- Fetch an inversion file system block.
  *
@@ -591,8 +629,13 @@ inv_fetchtup(LargeObjectDesc *obj_desc, Buffer *bufP)
 		{
 			ScanKeyData skey;
 
+			/* 
+			 * As scan index may be prematurely closed (on commit),
+			 * we must use object current offset (was 0) to 
+			 * reinitialize the entry [ PA ].
+			 */
 			ScanKeyEntryInitialize(&skey, 0x0, 1, F_INT4GE,
-								   Int32GetDatum(0));
+					       Int32GetDatum(obj_desc->offset));
 			obj_desc->iscan =
 				index_beginscan(obj_desc->index_r,
 								(bool) 0, (uint16) 1,
@@ -622,7 +665,7 @@ inv_fetchtup(LargeObjectDesc *obj_desc, Buffer *bufP)
 
 		/* remember this tid -- we may need it for later reads/writes */
 		ItemPointerCopy(&(res->heap_iptr), &(obj_desc->htid));
-
+		pfree(res);
 	}
 	else
 	{
@@ -1179,6 +1222,7 @@ _inv_getsize(Relation hreln, TupleDesc hdesc, Relation ireln)
 		if (res == (RetrieveIndexResult) NULL)
 		{
 			index_endscan(iscan);
+			pfree(iscan);
 			return (0);
 		}
 
@@ -1192,11 +1236,13 @@ _inv_getsize(Relation hreln, TupleDesc hdesc, Relation ireln)
 			ReleaseBuffer(buf);
 
 		htup = heap_fetch(hreln, false, &(res->heap_iptr), &buf);
+		pfree(res);
 
 	} while (!HeapTupleIsValid(htup));
 
 	/* don't need the index scan anymore */
 	index_endscan(iscan);
+	pfree(iscan);
 
 	/* get olastbyte attribute */
 	d = heap_getattr(htup, 1, hdesc, &isNull);

src/include/libpq/be-fsstubs.h

@@ -6,7 +6,7 @@
  *
  * Copyright (c) 1994, Regents of the University of California
  *
- * $Id: be-fsstubs.h,v 1.5 1997/09/08 21:52:33 momjian Exp $
+ * $Id: be-fsstubs.h,v 1.6 1998/07/21 04:17:26 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -37,4 +37,9 @@ extern int	lo_unlink(Oid lobjId);
 extern struct varlena *loread(int fd, int len);
 extern int	lowrite(int fd, struct varlena * wbuf);
 
+/*
+ * Added for buffer leak prevention [ Pascal André <andre@via.ecp.fr> ]
+ */
+extern void _lo_commit(void);
+
 #endif							/* BE_FSSTUBS_H */

src/include/storage/large_object.h

@@ -7,7 +7,7 @@
  *
  * Copyright (c) 1994, Regents of the University of California
  *
- * $Id: large_object.h,v 1.7 1997/09/08 21:54:29 momjian Exp $
+ * $Id: large_object.h,v 1.8 1998/07/21 04:17:30 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -54,4 +54,7 @@ extern int	inv_tell(LargeObjectDesc *obj_desc);
 extern int	inv_read(LargeObjectDesc *obj_desc, char *buf, int nbytes);
 extern int	inv_write(LargeObjectDesc *obj_desc, char *buf, int nbytes);
 
+/* added for buffer leak prevention [ PA ] */
+extern void inv_cleanindex(LargeObjectDesc *obj_desc);
+
 #endif							/* LARGE_OBJECT_H */