 DECLARE
     result system.job_type;
 BEGIN
-    IF pg_try_advisory_lock(0) THEN
+    IF pg_try_advisory_xact_lock(0) THEN
         SELECT job.id, job.type, job.description, job.size, js.config INTO result
             FROM system.job_queue
             JOIN system.job ON job_id = id

    result integer;
BEGIN
    -- Acquire locks
    LOCK TABLE system.job IN ACCESS EXCLUSIVE MODE;
    LOCK TABLE system.job_queue IN ACCESS EXCLUSIVE MODE;
    LOCK TABLE transform.state IN ACCESS EXCLUSIVE MODE;

    -- Drop constraints on dependent tables
    ALTER TABLE system.job_queue DROP CONSTRAINT job_queue_job_id_fkey;


            DELETE FROM system.job_queue WHERE job_id = result.id;
        END IF;

        RETURN result;
    ELSE
