Have “select for update” block on nonrexisting rows

Question

we have some persistent data in an application, that is queried from a server and then stored in a database so we can keep track of additional information. Because we do not wan

Answer 1

Example solution (i haven't found better :/)

Thread A:

BEGIN;
SELECT pg_advisory_xact_lock(42); -- database semaphore arbitrary ID
SELECT * FROM t WHERE id = 1;
DELETE FROM t WHERE id = 1;
INSERT INTO t (id, value) VALUES (1, 'thread A');
SELECT 1 FROM pg_sleep(10); -- only for race condition simulation
COMMIT;

Thread B:

BEGIN;
SELECT pg_advisory_xact_lock(42); -- database semaphore arbitrary ID
SELECT * FROM t WHERE id = 1;
DELETE FROM t WHERE id = 1;
INSERT INTO t (id, value) VALUES (1, 'thread B');
SELECT 1 FROM pg_sleep(10); -- only for race condition simulation
COMMIT;

Causes always correct order of transactions execution.