Change SearchSysCache coding conventions so that a reference count is

maintained for each cache entry.  A cache entry will not be freed until
the matching ReleaseSysCache call has been executed.  This eliminates
worries about cache entries getting dropped while still in use.  See
my posting to pg-hackers of even date for more info.

1 files changed, 50 insertions, 55 deletions

diff --git a/src/backend/commands/comment.c b/src/backend/commands/comment.c
index bff2b897c6e..8ab997831b9 100644
--- a/src/backend/commands/comment.c
+++ b/src/backend/commands/comment.c
@@ -276,7 +276,6 @@ DeleteComments(Oid oid)
 static void
 CommentRelation(int reltype, char *relname, char *comment)
 {
-
 	HeapTuple	reltuple;
 	Oid			oid;
 	char		relkind;
@@ -288,17 +287,20 @@ CommentRelation(int reltype, char *relname, char *comment)
 
 	/*** Now, attempt to find the oid in the cached version of pg_class ***/
 
-	reltuple = SearchSysCacheTuple(RELNAME, PointerGetDatum(relname),
-								   0, 0, 0);
+	reltuple = SearchSysCache(RELNAME,
+							  PointerGetDatum(relname),
+							  0, 0, 0);
 	if (!HeapTupleIsValid(reltuple))
 		elog(ERROR, "relation '%s' does not exist", relname);
 
 	oid = reltuple->t_data->t_oid;
 
-	/*** Next, verify that the relation type matches the intent ***/
-
 	relkind = ((Form_pg_class) GETSTRUCT(reltuple))->relkind;
 
+	ReleaseSysCache(reltuple);
+
+	/*** Next, verify that the relation type matches the intent ***/
+
 	switch (reltype)
 	{
 		case (INDEX):
@@ -322,7 +324,6 @@ CommentRelation(int reltype, char *relname, char *comment)
 	/*** Create the comments using the tuple's oid ***/
 
 	CreateComments(oid, comment);
-
 }
 
 /*------------------------------------------------------------------
@@ -340,9 +341,7 @@ CommentRelation(int reltype, char *relname, char *comment)
 static void
 CommentAttribute(char *relname, char *attrname, char *comment)
 {
-
 	Relation	relation;
-	HeapTuple	attrtuple;
 	Oid			oid;
 
 	/*** First, check object security ***/
@@ -350,15 +349,19 @@ CommentAttribute(char *relname, char *attrname, char *comment)
 	if (!pg_ownercheck(GetUserId(), relname, RELNAME))
 		elog(ERROR, "you are not permitted to comment on class '%s\'", relname);
 
-	/*** Now, fetch the attribute oid from the system cache ***/
+	/* Open the containing relation to ensure it won't go away meanwhile */
 
 	relation = heap_openr(relname, AccessShareLock);
-	attrtuple = SearchSysCacheTuple(ATTNAME, ObjectIdGetDatum(relation->rd_id),
-									PointerGetDatum(attrname), 0, 0);
-	if (!HeapTupleIsValid(attrtuple))
+
+	/*** Now, fetch the attribute oid from the system cache ***/
+
+	oid = GetSysCacheOid(ATTNAME,
+						 ObjectIdGetDatum(relation->rd_id),
+						 PointerGetDatum(attrname),
+						 0, 0);
+	if (!OidIsValid(oid))
 		elog(ERROR, "'%s' is not an attribute of class '%s'",
 			 attrname, relname);
-	oid = attrtuple->t_data->t_oid;
 
 	/*** Call CreateComments() to create/drop the comments ***/
 
@@ -412,11 +415,13 @@ CommentDatabase(char *database, char *comment)
 	/*** Now, fetch user information ***/
 
 	userid = GetUserId();
-	usertuple = SearchSysCacheTuple(SHADOWSYSID, ObjectIdGetDatum(userid),
-									0, 0, 0);
+	usertuple = SearchSysCache(SHADOWSYSID,
+							   ObjectIdGetDatum(userid),
+							   0, 0, 0);
 	if (!HeapTupleIsValid(usertuple))
 		elog(ERROR, "invalid user id %u", (unsigned) userid);
 	superuser = ((Form_pg_shadow) GETSTRUCT(usertuple))->usesuper;
+	ReleaseSysCache(usertuple);
 
 	/*** Allow if the userid matches the database dba or is a superuser ***/
 
@@ -452,8 +457,6 @@ CommentDatabase(char *database, char *comment)
 static void
 CommentRewrite(char *rule, char *comment)
 {
-
-	HeapTuple	rewritetuple;
 	Oid			oid;
 	char	   *relation;
 	int			aclcheck;
@@ -472,17 +475,15 @@ CommentRewrite(char *rule, char *comment)
 
 	/*** Next, find the rule's oid ***/
 
-	rewritetuple = SearchSysCacheTuple(RULENAME, PointerGetDatum(rule),
-									   0, 0, 0);
-	if (!HeapTupleIsValid(rewritetuple))
+	oid = GetSysCacheOid(RULENAME,
+						 PointerGetDatum(rule),
+						 0, 0, 0);
+	if (!OidIsValid(oid))
 		elog(ERROR, "rule '%s' does not exist", rule);
 
-	oid = rewritetuple->t_data->t_oid;
-
 	/*** Call CreateComments() to create/drop the comments ***/
 
 	CreateComments(oid, comment);
-
 }
 
 /*------------------------------------------------------------------
@@ -499,8 +500,6 @@ CommentRewrite(char *rule, char *comment)
 static void
 CommentType(char *type, char *comment)
 {
-
-	HeapTuple	typetuple;
 	Oid			oid;
 
 	/*** First, validate user ***/
@@ -515,17 +514,15 @@ CommentType(char *type, char *comment)
 
 	/*** Next, find the type's oid ***/
 
-	typetuple = SearchSysCacheTuple(TYPENAME, PointerGetDatum(type),
-									0, 0, 0);
-	if (!HeapTupleIsValid(typetuple))
+	oid = GetSysCacheOid(TYPENAME,
+						 PointerGetDatum(type),
+						 0, 0, 0);
+	if (!OidIsValid(oid))
 		elog(ERROR, "type '%s' does not exist", type);
 
-	oid = typetuple->t_data->t_oid;
-
 	/*** Call CreateComments() to create/drop the comments ***/
 
 	CreateComments(oid, comment);
-
 }
 
 /*------------------------------------------------------------------
@@ -543,7 +540,6 @@ CommentAggregate(char *aggregate, List *arguments, char *comment)
 {
 	TypeName   *aggtype = (TypeName *) lfirst(arguments);
 	char	   *aggtypename = NULL;
-	HeapTuple	aggtuple;
 	Oid			baseoid,
 				oid;
 	bool		defined;
@@ -580,9 +576,11 @@ CommentAggregate(char *aggregate, List *arguments, char *comment)
 
 	/*** Now, attempt to find the actual tuple in pg_aggregate ***/
 
-	aggtuple = SearchSysCacheTuple(AGGNAME, PointerGetDatum(aggregate),
-								   ObjectIdGetDatum(baseoid), 0, 0);
-	if (!HeapTupleIsValid(aggtuple))
+	oid = GetSysCacheOid(AGGNAME,
+						 PointerGetDatum(aggregate),
+						 ObjectIdGetDatum(baseoid),
+						 0, 0);
+	if (!OidIsValid(oid))
 	{
 		if (aggtypename)
 		{
@@ -593,12 +591,9 @@ CommentAggregate(char *aggregate, List *arguments, char *comment)
 			elog(ERROR, "aggregate '%s' does not exist", aggregate);
 	}
 
-	oid = aggtuple->t_data->t_oid;
-
 	/*** Call CreateComments() to create/drop the comments ***/
 
 	CreateComments(oid, comment);
-
 }
 
 /*------------------------------------------------------------------
@@ -615,8 +610,6 @@ CommentAggregate(char *aggregate, List *arguments, char *comment)
 static void
 CommentProc(char *function, List *arguments, char *comment)
 {
-	HeapTuple	argtuple,
-				functuple;
 	Oid			oid,
 				argoids[FUNC_MAX_ARGS];
 	int			i,
@@ -640,12 +633,11 @@ CommentProc(char *function, List *arguments, char *comment)
 			argoids[i] = InvalidOid;
 		else
 		{
-			argtuple = SearchSysCacheTuple(TYPENAME,
-										   PointerGetDatum(typnam),
-										   0, 0, 0);
-			if (!HeapTupleIsValid(argtuple))
+			argoids[i] = GetSysCacheOid(TYPENAME,
+										PointerGetDatum(typnam),
+										0, 0, 0);
+			if (!OidIsValid(argoids[i]))
 				elog(ERROR, "CommentProc: type '%s' not found", typnam);
-			argoids[i] = argtuple->t_data->t_oid;
 		}
 	}
 
@@ -659,14 +651,14 @@ CommentProc(char *function, List *arguments, char *comment)
 
 	/*** Now, find the corresponding oid for this procedure ***/
 
-	functuple = SearchSysCacheTuple(PROCNAME, PointerGetDatum(function),
-									Int32GetDatum(argcount),
-									PointerGetDatum(argoids), 0);
-	if (!HeapTupleIsValid(functuple))
+	oid = GetSysCacheOid(PROCNAME,
+						 PointerGetDatum(function),
+						 Int32GetDatum(argcount),
+						 PointerGetDatum(argoids),
+						 0);
+	if (!OidIsValid(oid))
 		func_error("CommentProc", function, argcount, argoids, NULL);
 
-	oid = functuple->t_data->t_oid;
-
 	/*** Call CreateComments() to create/drop the comments ***/
 
 	CreateComments(oid, comment);
@@ -738,10 +730,11 @@ CommentOperator(char *opername, List *arguments, char *comment)
 
 	/*** Attempt to fetch the operator oid ***/
 
-	optuple = SearchSysCacheTupleCopy(OPERNAME, PointerGetDatum(opername),
-									  ObjectIdGetDatum(leftoid),
-									  ObjectIdGetDatum(rightoid),
-									  CharGetDatum(oprtype));
+	optuple = SearchSysCache(OPERNAME,
+							 PointerGetDatum(opername),
+							 ObjectIdGetDatum(leftoid),
+							 ObjectIdGetDatum(rightoid),
+							 CharGetDatum(oprtype));
 	if (!HeapTupleIsValid(optuple))
 		elog(ERROR, "operator '%s' does not exist", opername);
 
@@ -764,6 +757,8 @@ CommentOperator(char *opername, List *arguments, char *comment)
 	if (oid == InvalidOid)
 		elog(ERROR, "operator '%s' does not have an underlying function", opername);
 
+	ReleaseSysCache(optuple);
+
 	/*** Call CreateComments() to create/drop the comments ***/
 
 	CreateComments(oid, comment);