--- build-tree/postgresql-8.0.3/src/backend/commands/user.c.orig	2005-10-14 11:00:16.000000000 +1300
+++ build-tree/postgresql-8.0.3/src/backend/commands/user.c	2005-10-14 11:01:09.000000000 +1300
@@ -17,6 +17,7 @@
 #include <errno.h>
 #include <unistd.h>
 
+#include "access/genam.h"
 #include "access/heapam.h"
 #include "catalog/catname.h"
 #include "catalog/indexing.h"
@@ -154,6 +155,27 @@
 	HeapScanDesc scan;
 	HeapTuple	tuple;
 	TupleDesc	dsc = RelationGetDescr(grel);
+	/* Look up user names by user system id. */
+	Relation	urel = heap_openr(ShadowRelationName, AccessShareLock),
+				ureli = index_openr(ShadowSysidIndex);
+
+	/* Scan for system id equality. */
+	ScanKeyData ukey =
+	{
+		.sk_flags		= 0,
+		.sk_attno		= 1,
+		.sk_strategy	= BTEqualStrategyNumber,
+		.sk_subtype		= InvalidOid
+	};
+
+	/* We expect the first index column to be in order. */
+	Assert(Anum_pg_shadow_usesysid == ureli->rd_index->indkey[0]);
+
+	/* And only one system identifier column type. */
+	Assert(RelationGetDescr(urel)->attrs[Anum_pg_shadow_usesysid - 1]->atttypid == INT4OID);
+
+	/* Finish scan key initialisation. */
+	fmgr_info(F_INT4EQ, &ukey.sk_func);
 
 	/*
 	 * Create a temporary filename to be renamed later.  This prevents the
@@ -192,6 +214,7 @@
 					num;
 		char	   *usename;
 		bool		first_user = true;
+		IndexScanDesc userscan;
 
 		datum = heap_getattr(tuple, Anum_pg_group_groname, dsc, &isnull);
 		/* ignore NULL groupnames --- shouldn't happen */
@@ -221,11 +244,12 @@
 		/* scan grolist */
 		num = IDLIST_NUM(grolist_p);
 		aidp = IDLIST_DAT(grolist_p);
-		for (i = 0; i < num; ++i)
+		for (i = 0; i < num; ++i, index_endscan(userscan))
 		{
-			tuple = SearchSysCache(SHADOWSYSID,
-								   PointerGetDatum(aidp[i]),
-								   0, 0, 0);
+			ukey.sk_argument = PointerGetDatum(aidp[i]);
+			userscan = index_beginscan(urel, ureli, SnapshotSelf, 1, &ukey);
+			tuple = index_getnext(userscan, ForwardScanDirection);
+
 			if (HeapTupleIsValid(tuple))
 			{
 				usename = NameStr(((Form_pg_shadow) GETSTRUCT(tuple))->usename);
@@ -254,8 +278,6 @@
 
 				first_user = false;
 				fputs_quote(usename, fp);
-
-				ReleaseSysCache(tuple);
 			}
 		}
 		if (!first_user)
@@ -265,6 +287,8 @@
 			pfree(grolist_p);
 	}
 	heap_endscan(scan);
+	index_close(ureli);
+	heap_close(urel, AccessShareLock);
 
 	if (FreeFile(fp))
 		ereport(ERROR,