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                       
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                        
step wy4: UPDATE t SET txt = 'd' WHERE id = 500000;
step rz4: SELECT * FROM t WHERE id = 1;
id             txt            

1                             
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;