Parsed test spec with 2 sessions

starting permutation: s2a s1a s2b s2c s2d s2e s1b s2f
step s2a: SELECT pg_advisory_lock(0);
pg_advisory_lock
----------------
                
(1 row)

step s1a: SELECT * FROM foo WHERE pg_advisory_lock(0) IS NOT NULL FOR UPDATE NOWAIT; <waiting ...>
step s2b: UPDATE foo SET data = data;
step s2c: BEGIN;
step s2d: UPDATE foo SET data = data;
step s2e: SELECT pg_advisory_unlock(0);
pg_advisory_unlock
------------------
t                 
(1 row)

step s1a: <... completed>
ERROR:  could not serialize access due to concurrent update
step s1b: COMMIT;
step s2f: COMMIT;