--
-- Commit Timestamp
--
SHOW track_commit_timestamp;
 track_commit_timestamp 
------------------------
 on
(1 row)

CREATE TABLE committs_test(id serial, ts timestamptz default now());
INSERT INTO committs_test DEFAULT VALUES;
INSERT INTO committs_test DEFAULT VALUES;
INSERT INTO committs_test DEFAULT VALUES;
SELECT id,
       pg_xact_commit_timestamp(xmin) >= ts,
       pg_xact_commit_timestamp(xmin) <= now(),
       pg_xact_commit_timestamp(xmin) - ts < '60s' -- 60s should give a lot of reserve
FROM committs_test
ORDER BY id;
 id | ?column? | ?column? | ?column? 
----+----------+----------+----------
  1 | t        | t        | t
  2 | t        | t        | t
  3 | t        | t        | t
(3 rows)

DROP TABLE committs_test;
SELECT pg_xact_commit_timestamp('0'::xid);
ERROR:  cannot retrieve commit timestamp for transaction 0
SELECT pg_xact_commit_timestamp('1'::xid);
 pg_xact_commit_timestamp 
--------------------------
 
(1 row)

SELECT pg_xact_commit_timestamp('2'::xid);
 pg_xact_commit_timestamp 
--------------------------
 
(1 row)

SELECT x.xid::text::bigint > 0, x.timestamp > '-infinity'::timestamptz, x.timestamp <= now() FROM pg_last_committed_xact() x;
 ?column? | ?column? | ?column? 
----------+----------+----------
 t        | t        | t
(1 row)