Parsed test spec with 3 sessions

starting permutation: s0_vacuum s1_plan s1_fetches s1_begin s2_begin s1_read s2_read s1_update s2_update s1_commit s2_commit
step s0_vacuum: VACUUM bsp;
step s1_plan: EXPLAIN (COSTS OFF) SELECT count(*), sum(id) FROM bsp WHERE c = 1;
QUERY PLAN                                                   
-------------------------------------------------------------
Finalize Aggregate                                           
  ->  Gather                                                 
        Workers Planned: 2                                   
        ->  Partial Aggregate                                
              ->  Parallel Custom Scan (LionBtreeScan) on bsp
                    Index: bsp_k (index only)                
                    Lion Cond: (c = 1)                       
                    Lion Indexes: bsp_c                      
(8 rows)

step s1_fetches: SELECT bsp_fetches('SELECT count(*), sum(id) FROM bsp WHERE c = 1');
bsp_fetches                                                                            
---------------------------------------------------------------------------------------
Parallel Custom Scan (LionBtreeScan) on bsp; Index: bsp_k (index only); Heap Fetches: 0
(1 row)

step s1_begin: BEGIN ISOLATION LEVEL SERIALIZABLE;
step s2_begin: BEGIN ISOLATION LEVEL SERIALIZABLE;
step s1_read: SELECT count(*), sum(id) FROM bsp WHERE c = 1;
count|   sum
-----+------
  300|448800
(1 row)

step s2_read: SELECT count(*), sum(id) FROM bsp WHERE c = 2;
count|   sum
-----+------
  300|449100
(1 row)

step s1_update: UPDATE bsp SET note = 's1' WHERE id = 82;
step s2_update: UPDATE bsp SET note = 's2' WHERE id = 191;
step s1_commit: COMMIT;
step s2_commit: COMMIT;
ERROR:  could not serialize access due to read/write dependencies among transactions

starting permutation: s0_vacuum s1_begin s2_begin s1_read s2_read s1_update s1_commit s2_update s2_commit
step s0_vacuum: VACUUM bsp;
step s1_begin: BEGIN ISOLATION LEVEL SERIALIZABLE;
step s2_begin: BEGIN ISOLATION LEVEL SERIALIZABLE;
step s1_read: SELECT count(*), sum(id) FROM bsp WHERE c = 1;
count|   sum
-----+------
  300|448800
(1 row)

step s2_read: SELECT count(*), sum(id) FROM bsp WHERE c = 2;
count|   sum
-----+------
  300|449100
(1 row)

step s1_update: UPDATE bsp SET note = 's1' WHERE id = 82;
step s1_commit: COMMIT;
step s2_update: UPDATE bsp SET note = 's2' WHERE id = 191;
ERROR:  could not serialize access due to read/write dependencies among transactions
step s2_commit: COMMIT;