Improve behavior of concurrent ALTER <relation> .. SET SCHEMA.

If the referrent of a name changes while we're waiting for the lock,
we must recheck permissons.  We also now check the relkind before
locking, since it's easy to do that long the way.

Patch by me; review by Noah Misch.

src/backend/commands/alter.c

@@ -191,7 +191,6 @@ ExecAlterObjectSchemaStmt(AlterObjectSchemaStmt *stmt)
 		case OBJECT_TABLE:
 		case OBJECT_VIEW:
 		case OBJECT_FOREIGN_TABLE:
-			CheckRelationOwnership(stmt->relation, true);
 			AlterTableNamespace(stmt->relation, stmt->newschema,
 								stmt->objectType, AccessExclusiveLock);
 			break;

src/backend/commands/tablecmds.c

@@ -9379,28 +9379,35 @@ ATExecGenericOptions(Relation rel, List *options)
 	heap_freetuple(tuple);
 }
 
-
 /*
- * Execute ALTER TABLE SET SCHEMA
- *
- * Note: caller must have checked ownership of the relation already
+ * Perform permissions and integrity checks before acquiring a relation lock.
  */
-void
-AlterTableNamespace(RangeVar *relation, const char *newschema,
-					ObjectType stmttype, LOCKMODE lockmode)
+static void
+RangeVarCallbackForAlterTableNamespace(const RangeVar *rv, Oid relid,
+									   Oid oldrelid, void *arg)
 {
-	Relation	rel;
-	Oid			relid;
-	Oid			oldNspOid;
-	Oid			nspOid;
-	Relation	classRel;
+	HeapTuple		tuple;
+	Form_pg_class	form;
+	ObjectType		stmttype;
+
+	tuple = SearchSysCache1(RELOID, ObjectIdGetDatum(relid));
+	if (!HeapTupleIsValid(tuple))
+		return;							/* concurrently dropped */
+	form = (Form_pg_class) GETSTRUCT(tuple);
 
-	rel = relation_openrv(relation, lockmode);
+	/* Must own table. */
+	if (!pg_class_ownercheck(relid, GetUserId()))
+		aclcheck_error(ACLCHECK_NOT_OWNER, ACL_KIND_CLASS, rv->relname);
 
-	relid = RelationGetRelid(rel);
-	oldNspOid = RelationGetNamespace(rel);
+	/* No system table modifications unless explicitly allowed. */
+	if (!allowSystemTableMods && IsSystemClass(form))
+		ereport(ERROR,
+				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+				 errmsg("permission denied: \"%s\" is a system catalog",
+						rv->relname)));
 
 	/* Check relation type against type specified in the ALTER command */
+	stmttype = * (ObjectType *) arg;
 	switch (stmttype)
 	{
 		case OBJECT_TABLE:
@@ -9412,27 +9419,24 @@ AlterTableNamespace(RangeVar *relation, const char *newschema,
 			break;
 
 		case OBJECT_SEQUENCE:
-			if (rel->rd_rel->relkind != RELKIND_SEQUENCE)
+			if (form->relkind != RELKIND_SEQUENCE)
 				ereport(ERROR,
 						(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-						 errmsg("\"%s\" is not a sequence",
-								RelationGetRelationName(rel))));
+						 errmsg("\"%s\" is not a sequence", rv->relname)));
 			break;
 
 		case OBJECT_VIEW:
-			if (rel->rd_rel->relkind != RELKIND_VIEW)
+			if (form->relkind != RELKIND_VIEW)
 				ereport(ERROR,
 						(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-						 errmsg("\"%s\" is not a view",
-								RelationGetRelationName(rel))));
+						 errmsg("\"%s\" is not a view", rv->relname)));
 			break;
 
 		case OBJECT_FOREIGN_TABLE:
-			if (rel->rd_rel->relkind != RELKIND_FOREIGN_TABLE)
+			if (form->relkind != RELKIND_FOREIGN_TABLE)
 				ereport(ERROR,
 						(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-						 errmsg("\"%s\" is not a foreign table",
-								RelationGetRelationName(rel))));
+						 errmsg("\"%s\" is not a foreign table", rv->relname)));
 			break;
 
 		default:
@@ -9440,33 +9444,18 @@ AlterTableNamespace(RangeVar *relation, const char *newschema,
 	}
 
 	/* Can we change the schema of this tuple? */
-	switch (rel->rd_rel->relkind)
+	switch (form->relkind)
 	{
 		case RELKIND_RELATION:
 		case RELKIND_VIEW:
+		case RELKIND_SEQUENCE:
 		case RELKIND_FOREIGN_TABLE:
 			/* ok to change schema */
 			break;
-		case RELKIND_SEQUENCE:
-			{
-				/* if it's an owned sequence, disallow moving it by itself */
-				Oid			tableId;
-				int32		colId;
-
-				if (sequenceIsOwned(relid, &tableId, &colId))
-					ereport(ERROR,
-							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-							 errmsg("cannot move an owned sequence into another schema"),
-					  errdetail("Sequence \"%s\" is linked to table \"%s\".",
-								RelationGetRelationName(rel),
-								get_rel_name(tableId))));
-			}
-			break;
 		case RELKIND_COMPOSITE_TYPE:
 			ereport(ERROR,
 					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-					 errmsg("\"%s\" is a composite type",
-							RelationGetRelationName(rel)),
+					 errmsg("\"%s\" is a composite type", rv->relname),
 					 errhint("Use ALTER TYPE instead.")));
 			break;
 		case RELKIND_INDEX:
@@ -9476,7 +9465,45 @@ AlterTableNamespace(RangeVar *relation, const char *newschema,
 			ereport(ERROR,
 					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
 			errmsg("\"%s\" is not a table, view, sequence, or foreign table",
-				   RelationGetRelationName(rel))));
+				   rv->relname)));
+	}
+
+	ReleaseSysCache(tuple);
+}
+
+/*
+ * Execute ALTER TABLE SET SCHEMA
+ */
+void
+AlterTableNamespace(RangeVar *relation, const char *newschema,
+					ObjectType stmttype, LOCKMODE lockmode)
+{
+	Relation	rel;
+	Oid			relid;
+	Oid			oldNspOid;
+	Oid			nspOid;
+	Relation	classRel;
+
+	relid = RangeVarGetRelidExtended(relation, lockmode, false, false,
+									 RangeVarCallbackForAlterTableNamespace,
+									 (void *) &stmttype);
+	rel = relation_open(relid, NoLock);
+
+	oldNspOid = RelationGetNamespace(rel);
+
+	/* If it's an owned sequence, disallow moving it by itself. */
+	if (rel->rd_rel->relkind == RELKIND_SEQUENCE)
+	{
+		Oid			tableId;
+		int32		colId;
+
+		if (sequenceIsOwned(relid, &tableId, &colId))
+			ereport(ERROR,
+					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					 errmsg("cannot move an owned sequence into another schema"),
+			  errdetail("Sequence \"%s\" is linked to table \"%s\".",
+						RelationGetRelationName(rel),
+						get_rel_name(tableId))));
 	}
 
 	/* get schema OID and check its permissions */