Parsed test spec with 4 sessions

starting permutation: rx1 wx2 c2 wx3 ry3 wy4 rz4 c4 c3 wz1 c1
step rx1: SELECT * FROM t WHERE id = 1000000;
     id|txt
-------+---
1000000|   
(1 row)

step wx2: UPDATE t SET txt = 'b' WHERE id = 1000000;
step c2: COMMIT;
step wx3: UPDATE t SET txt = 'c' WHERE id = 1000000;
step ry3: SELECT * FROM t WHERE id = 500000;
    id|txt
------+---
500000|   
(1 row)

step wy4: UPDATE t SET txt = 'd' WHERE id = 500000;
step rz4: SELECT * FROM t WHERE id = 1;
id|txt
--+---
 1|   
(1 row)

step c4: COMMIT;
step c3: COMMIT;
step wz1: UPDATE t SET txt = 'a' WHERE id = 1;
ERROR:  could not serialize access due to read/write dependencies among transactions
step c1: COMMIT;