Parsed test spec with 2 sessions

starting permutation: s1f1 s1sleep s2u s1f2
step s1f1: SELECT c FROM sto1 ORDER BY c LIMIT 1;
c
-
1
(1 row)

step s1sleep: SELECT setting, pg_sleep(6) FROM pg_settings WHERE name = 'old_snapshot_threshold';
setting|pg_sleep
-------+--------
      0|        
(1 row)

step s2u: UPDATE sto1 SET c = 1001 WHERE c = 1;
step s1f2: SELECT c FROM sto1 ORDER BY c LIMIT 1;
ERROR:  snapshot too old