action buffer bug 6356566 busy cascade cbo child column cost data dba_job dbms_application_info dbms_job decode developer enq enq: tm - contention execution plan explain plan foreign key full table scan function based index guest histogram ignite index insert IS NULL jobs not running job_queue locking logon trigger method_opt module NVL object optimizer ora-12152 oracle Oracle bug 3427424 parent pl/sql plans predicate primary procedure query tuning referential integrity set_module skew sql tuning table lock top tuning unindexed foreign key constraint update v$sql_plan wait event _cursor_plan_unparse_enabled