Arrange for the pg_foo_is_visible and has_foo_privilege families of functions

to return NULL, instead of erroring out, if the target object is specified by
OID and we can't find that OID in the catalogs.  Since these functions operate
internally on SnapshotNow rules, there is a race condition when using them
in user queries: the query's MVCC snapshot might "see" a catalog row that's
already committed dead, leading to a failure when the inquiry function is
applied.  Returning NULL should generally provide more convenient behavior.
This issue has been complained of before, and in particular we are now seeing
it in the regression tests due to another recent patch.

src/backend/catalog/namespace.c

@@ -13,7 +13,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/catalog/namespace.c,v 1.113 2008/12/04 17:51:26 petere Exp $
+ *	  $PostgreSQL: pgsql/src/backend/catalog/namespace.c,v 1.114 2008/12/15 18:09:40 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -3250,6 +3250,15 @@ fetch_search_path_array(Oid *sarray, int sarray_len)
 
 /*
  * Export the FooIsVisible functions as SQL-callable functions.
+ *
+ * Note: as of Postgres 8.4, these will silently return NULL if called on
+ * a nonexistent object OID, rather than failing.  This is to avoid race
+ * condition errors when a query that's scanning a catalog using an MVCC
+ * snapshot uses one of these functions.  The underlying IsVisible functions
+ * operate on SnapshotNow semantics and so might see the object as already
+ * gone when it's still visible to the MVCC snapshot.  (There is no race
+ * condition in the current coding because we don't accept sinval messages
+ * between the SearchSysCacheExists test and the subsequent lookup.)
  */
 
 Datum
@@ -3257,6 +3266,11 @@ pg_table_is_visible(PG_FUNCTION_ARGS)
 {
 	Oid			oid = PG_GETARG_OID(0);
 
+	if (!SearchSysCacheExists(RELOID,
+							  ObjectIdGetDatum(oid),
+							  0, 0, 0))
+		PG_RETURN_NULL();
+
 	PG_RETURN_BOOL(RelationIsVisible(oid));
 }
 
@@ -3265,6 +3279,11 @@ pg_type_is_visible(PG_FUNCTION_ARGS)
 {
 	Oid			oid = PG_GETARG_OID(0);
 
+	if (!SearchSysCacheExists(TYPEOID,
+							  ObjectIdGetDatum(oid),
+							  0, 0, 0))
+		PG_RETURN_NULL();
+
 	PG_RETURN_BOOL(TypeIsVisible(oid));
 }
 
@@ -3273,6 +3292,11 @@ pg_function_is_visible(PG_FUNCTION_ARGS)
 {
 	Oid			oid = PG_GETARG_OID(0);
 
+	if (!SearchSysCacheExists(PROCOID,
+							  ObjectIdGetDatum(oid),
+							  0, 0, 0))
+		PG_RETURN_NULL();
+
 	PG_RETURN_BOOL(FunctionIsVisible(oid));
 }
 
@@ -3281,6 +3305,11 @@ pg_operator_is_visible(PG_FUNCTION_ARGS)
 {
 	Oid			oid = PG_GETARG_OID(0);
 
+	if (!SearchSysCacheExists(OPEROID,
+							  ObjectIdGetDatum(oid),
+							  0, 0, 0))
+		PG_RETURN_NULL();
+
 	PG_RETURN_BOOL(OperatorIsVisible(oid));
 }
 
@@ -3289,6 +3318,11 @@ pg_opclass_is_visible(PG_FUNCTION_ARGS)
 {
 	Oid			oid = PG_GETARG_OID(0);
 
+	if (!SearchSysCacheExists(CLAOID,
+							  ObjectIdGetDatum(oid),
+							  0, 0, 0))
+		PG_RETURN_NULL();
+
 	PG_RETURN_BOOL(OpclassIsVisible(oid));
 }
 
@@ -3297,6 +3331,11 @@ pg_conversion_is_visible(PG_FUNCTION_ARGS)
 {
 	Oid			oid = PG_GETARG_OID(0);
 
+	if (!SearchSysCacheExists(CONVOID,
+							  ObjectIdGetDatum(oid),
+							  0, 0, 0))
+		PG_RETURN_NULL();
+
 	PG_RETURN_BOOL(ConversionIsVisible(oid));
 }
 
@@ -3305,6 +3344,11 @@ pg_ts_parser_is_visible(PG_FUNCTION_ARGS)
 {
 	Oid			oid = PG_GETARG_OID(0);
 
+	if (!SearchSysCacheExists(TSPARSEROID,
+							  ObjectIdGetDatum(oid),
+							  0, 0, 0))
+		PG_RETURN_NULL();
+
 	PG_RETURN_BOOL(TSParserIsVisible(oid));
 }
 
@@ -3313,6 +3357,11 @@ pg_ts_dict_is_visible(PG_FUNCTION_ARGS)
 {
 	Oid			oid = PG_GETARG_OID(0);
 
+	if (!SearchSysCacheExists(TSDICTOID,
+							  ObjectIdGetDatum(oid),
+							  0, 0, 0))
+		PG_RETURN_NULL();
+
 	PG_RETURN_BOOL(TSDictionaryIsVisible(oid));
 }
 
@@ -3321,6 +3370,11 @@ pg_ts_template_is_visible(PG_FUNCTION_ARGS)
 {
 	Oid			oid = PG_GETARG_OID(0);
 
+	if (!SearchSysCacheExists(TSTEMPLATEOID,
+							  ObjectIdGetDatum(oid),
+							  0, 0, 0))
+		PG_RETURN_NULL();
+
 	PG_RETURN_BOOL(TSTemplateIsVisible(oid));
 }
 
@@ -3329,6 +3383,11 @@ pg_ts_config_is_visible(PG_FUNCTION_ARGS)
 {
 	Oid			oid = PG_GETARG_OID(0);
 
+	if (!SearchSysCacheExists(TSCONFIGOID,
+							  ObjectIdGetDatum(oid),
+							  0, 0, 0))
+		PG_RETURN_NULL();
+
 	PG_RETURN_BOOL(TSConfigIsVisible(oid));
 }
 

src/backend/utils/adt/acl.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/adt/acl.c,v 1.142 2008/09/09 18:58:08 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/acl.c,v 1.143 2008/12/15 18:09:41 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1361,7 +1361,9 @@ convert_priv_string(text *priv_type_text)
  *		user name, user OID, or implicit user = current_user.
  *
  *		The result is a boolean value: true if user has the indicated
- *		privilege, false if not.
+ *		privilege, false if not.  The variants that take a relation OID
+ *		return NULL if the OID doesn't exist (rather than failing, as
+ *		they did before Postgres 8.4).
  */
 
 /*
@@ -1432,6 +1434,11 @@ has_table_privilege_name_id(PG_FUNCTION_ARGS)
 	roleid = get_roleid_checked(NameStr(*username));
 	mode = convert_table_priv_string(priv_type_text);
 
+	if (!SearchSysCacheExists(RELOID,
+							  ObjectIdGetDatum(tableoid),
+							  0, 0, 0))
+		PG_RETURN_NULL();
+
 	aclresult = pg_class_aclcheck(tableoid, roleid, mode);
 
 	PG_RETURN_BOOL(aclresult == ACLCHECK_OK);
@@ -1455,6 +1462,11 @@ has_table_privilege_id(PG_FUNCTION_ARGS)
 	roleid = GetUserId();
 	mode = convert_table_priv_string(priv_type_text);
 
+	if (!SearchSysCacheExists(RELOID,
+							  ObjectIdGetDatum(tableoid),
+							  0, 0, 0))
+		PG_RETURN_NULL();
+
 	aclresult = pg_class_aclcheck(tableoid, roleid, mode);
 
 	PG_RETURN_BOOL(aclresult == ACLCHECK_OK);
@@ -1499,6 +1511,11 @@ has_table_privilege_id_id(PG_FUNCTION_ARGS)
 
 	mode = convert_table_priv_string(priv_type_text);
 
+	if (!SearchSysCacheExists(RELOID,
+							  ObjectIdGetDatum(tableoid),
+							  0, 0, 0))
+		PG_RETURN_NULL();
+
 	aclresult = pg_class_aclcheck(tableoid, roleid, mode);
 
 	PG_RETURN_BOOL(aclresult == ACLCHECK_OK);
@@ -1587,7 +1604,7 @@ convert_table_priv_string(text *priv_type_text)
  *		user name, user OID, or implicit user = current_user.
  *
  *		The result is a boolean value: true if user has the indicated
- *		privilege, false if not.
+ *		privilege, false if not, or NULL if object doesn't exist.
  */
 
 /*
@@ -1658,6 +1675,11 @@ has_database_privilege_name_id(PG_FUNCTION_ARGS)
 	roleid = get_roleid_checked(NameStr(*username));
 	mode = convert_database_priv_string(priv_type_text);
 
+	if (!SearchSysCacheExists(DATABASEOID,
+							  ObjectIdGetDatum(databaseoid),
+							  0, 0, 0))
+		PG_RETURN_NULL();
+
 	aclresult = pg_database_aclcheck(databaseoid, roleid, mode);
 
 	PG_RETURN_BOOL(aclresult == ACLCHECK_OK);
@@ -1681,6 +1703,11 @@ has_database_privilege_id(PG_FUNCTION_ARGS)
 	roleid = GetUserId();
 	mode = convert_database_priv_string(priv_type_text);
 
+	if (!SearchSysCacheExists(DATABASEOID,
+							  ObjectIdGetDatum(databaseoid),
+							  0, 0, 0))
+		PG_RETURN_NULL();
+
 	aclresult = pg_database_aclcheck(databaseoid, roleid, mode);
 
 	PG_RETURN_BOOL(aclresult == ACLCHECK_OK);
@@ -1725,6 +1752,11 @@ has_database_privilege_id_id(PG_FUNCTION_ARGS)
 
 	mode = convert_database_priv_string(priv_type_text);
 
+	if (!SearchSysCacheExists(DATABASEOID,
+							  ObjectIdGetDatum(databaseoid),
+							  0, 0, 0))
+		PG_RETURN_NULL();
+
 	aclresult = pg_database_aclcheck(databaseoid, roleid, mode);
 
 	PG_RETURN_BOOL(aclresult == ACLCHECK_OK);
@@ -1798,7 +1830,7 @@ convert_database_priv_string(text *priv_type_text)
  *		user name, user OID, or implicit user = current_user.
  *
  *		The result is a boolean value: true if user has the indicated
- *		privilege, false if not.
+ *		privilege, false if not, or NULL if object doesn't exist.
  */
 
 /*
@@ -1869,6 +1901,11 @@ has_function_privilege_name_id(PG_FUNCTION_ARGS)
 	roleid = get_roleid_checked(NameStr(*username));
 	mode = convert_function_priv_string(priv_type_text);
 
+	if (!SearchSysCacheExists(PROCOID,
+							  ObjectIdGetDatum(functionoid),
+							  0, 0, 0))
+		PG_RETURN_NULL();
+
 	aclresult = pg_proc_aclcheck(functionoid, roleid, mode);
 
 	PG_RETURN_BOOL(aclresult == ACLCHECK_OK);
@@ -1892,6 +1929,11 @@ has_function_privilege_id(PG_FUNCTION_ARGS)
 	roleid = GetUserId();
 	mode = convert_function_priv_string(priv_type_text);
 
+	if (!SearchSysCacheExists(PROCOID,
+							  ObjectIdGetDatum(functionoid),
+							  0, 0, 0))
+		PG_RETURN_NULL();
+
 	aclresult = pg_proc_aclcheck(functionoid, roleid, mode);
 
 	PG_RETURN_BOOL(aclresult == ACLCHECK_OK);
@@ -1936,6 +1978,11 @@ has_function_privilege_id_id(PG_FUNCTION_ARGS)
 
 	mode = convert_function_priv_string(priv_type_text);
 
+	if (!SearchSysCacheExists(PROCOID,
+							  ObjectIdGetDatum(functionoid),
+							  0, 0, 0))
+		PG_RETURN_NULL();
+
 	aclresult = pg_proc_aclcheck(functionoid, roleid, mode);
 
 	PG_RETURN_BOOL(aclresult == ACLCHECK_OK);
@@ -1996,7 +2043,7 @@ convert_function_priv_string(text *priv_type_text)
  *		user name, user OID, or implicit user = current_user.
  *
  *		The result is a boolean value: true if user has the indicated
- *		privilege, false if not.
+ *		privilege, false if not, or NULL if object doesn't exist.
  */
 
 /*
@@ -2067,6 +2114,11 @@ has_language_privilege_name_id(PG_FUNCTION_ARGS)
 	roleid = get_roleid_checked(NameStr(*username));
 	mode = convert_language_priv_string(priv_type_text);
 
+	if (!SearchSysCacheExists(LANGOID,
+							  ObjectIdGetDatum(languageoid),
+							  0, 0, 0))
+		PG_RETURN_NULL();
+
 	aclresult = pg_language_aclcheck(languageoid, roleid, mode);
 
 	PG_RETURN_BOOL(aclresult == ACLCHECK_OK);
@@ -2090,6 +2142,11 @@ has_language_privilege_id(PG_FUNCTION_ARGS)
 	roleid = GetUserId();
 	mode = convert_language_priv_string(priv_type_text);
 
+	if (!SearchSysCacheExists(LANGOID,
+							  ObjectIdGetDatum(languageoid),
+							  0, 0, 0))
+		PG_RETURN_NULL();
+
 	aclresult = pg_language_aclcheck(languageoid, roleid, mode);
 
 	PG_RETURN_BOOL(aclresult == ACLCHECK_OK);
@@ -2134,6 +2191,11 @@ has_language_privilege_id_id(PG_FUNCTION_ARGS)
 
 	mode = convert_language_priv_string(priv_type_text);
 
+	if (!SearchSysCacheExists(LANGOID,
+							  ObjectIdGetDatum(languageoid),
+							  0, 0, 0))
+		PG_RETURN_NULL();
+
 	aclresult = pg_language_aclcheck(languageoid, roleid, mode);
 
 	PG_RETURN_BOOL(aclresult == ACLCHECK_OK);
@@ -2194,7 +2256,7 @@ convert_language_priv_string(text *priv_type_text)
  *		user name, user OID, or implicit user = current_user.
  *
  *		The result is a boolean value: true if user has the indicated
- *		privilege, false if not.
+ *		privilege, false if not, or NULL if object doesn't exist.
  */
 
 /*
@@ -2265,6 +2327,11 @@ has_schema_privilege_name_id(PG_FUNCTION_ARGS)
 	roleid = get_roleid_checked(NameStr(*username));
 	mode = convert_schema_priv_string(priv_type_text);
 
+	if (!SearchSysCacheExists(NAMESPACEOID,
+							  ObjectIdGetDatum(schemaoid),
+							  0, 0, 0))
+		PG_RETURN_NULL();
+
 	aclresult = pg_namespace_aclcheck(schemaoid, roleid, mode);
 
 	PG_RETURN_BOOL(aclresult == ACLCHECK_OK);
@@ -2288,6 +2355,11 @@ has_schema_privilege_id(PG_FUNCTION_ARGS)
 	roleid = GetUserId();
 	mode = convert_schema_priv_string(priv_type_text);
 
+	if (!SearchSysCacheExists(NAMESPACEOID,
+							  ObjectIdGetDatum(schemaoid),
+							  0, 0, 0))
+		PG_RETURN_NULL();
+
 	aclresult = pg_namespace_aclcheck(schemaoid, roleid, mode);
 
 	PG_RETURN_BOOL(aclresult == ACLCHECK_OK);
@@ -2332,6 +2404,11 @@ has_schema_privilege_id_id(PG_FUNCTION_ARGS)
 
 	mode = convert_schema_priv_string(priv_type_text);
 
+	if (!SearchSysCacheExists(NAMESPACEOID,
+							  ObjectIdGetDatum(schemaoid),
+							  0, 0, 0))
+		PG_RETURN_NULL();
+
 	aclresult = pg_namespace_aclcheck(schemaoid, roleid, mode);
 
 	PG_RETURN_BOOL(aclresult == ACLCHECK_OK);

src/test/regress/expected/privileges.out

@@ -321,7 +321,11 @@ ERROR:  unrecognized privilege type: "sel"
 select has_table_privilege(-999999,'pg_authid','update');
 ERROR:  role with OID 4293967297 does not exist
 select has_table_privilege(1,'select');
-ERROR:  relation with OID 1 does not exist
+ has_table_privilege 
+---------------------
+ 
+(1 row)
+
 -- superuser
 \c -
 select has_table_privilege(current_user,'pg_authid','select');