Parsed test spec with 2 sessions

starting permutation: s2check s1b s2b s1i s2summ s1c s2c s2check
step s2check: SELECT * FROM brin_page_items(get_raw_page('brinidx', 2), 'brinidx'::regclass);
itemoffset|blknum|attnum|allnulls|hasnulls|placeholder|value   
----------+------+------+--------+--------+-----------+--------
         1|     0|     1|f       |t       |f          |{1 .. 1}
(1 row)

step s1b: BEGIN ISOLATION LEVEL REPEATABLE READ;
step s2b: BEGIN ISOLATION LEVEL REPEATABLE READ; SELECT 1;
?column?
--------
       1
(1 row)

step s1i: INSERT INTO brin_iso VALUES (1000);
step s2summ: SELECT brin_summarize_new_values('brinidx'::regclass);
brin_summarize_new_values
-------------------------
                        1
(1 row)

step s1c: COMMIT;
step s2c: COMMIT;
step s2check: SELECT * FROM brin_page_items(get_raw_page('brinidx', 2), 'brinidx'::regclass);
itemoffset|blknum|attnum|allnulls|hasnulls|placeholder|value      
----------+------+------+--------+--------+-----------+-----------
         1|     0|     1|f       |t       |f          |{1 .. 1}   
         2|     1|     1|f       |f       |f          |{1 .. 1000}
(2 rows)


starting permutation: s2check s1b s1i s2vacuum s1c s2check
step s2check: SELECT * FROM brin_page_items(get_raw_page('brinidx', 2), 'brinidx'::regclass);
itemoffset|blknum|attnum|allnulls|hasnulls|placeholder|value   
----------+------+------+--------+--------+-----------+--------
         1|     0|     1|f       |t       |f          |{1 .. 1}
(1 row)

step s1b: BEGIN ISOLATION LEVEL REPEATABLE READ;
step s1i: INSERT INTO brin_iso VALUES (1000);
step s2vacuum: VACUUM brin_iso;
step s1c: COMMIT;
step s2check: SELECT * FROM brin_page_items(get_raw_page('brinidx', 2), 'brinidx'::regclass);
itemoffset|blknum|attnum|allnulls|hasnulls|placeholder|value      
----------+------+------+--------+--------+-----------+-----------
         1|     0|     1|f       |t       |f          |{1 .. 1}   
         2|     1|     1|f       |f       |f          |{1 .. 1000}
(2 rows)