background query not executed with pg_background_detach(pg_background_launch('...'))

[radist-nt]

Steps to reproduce the problem:

1. Open two sessions for database (S1 and S2)
2. Execute LISTEN test_background; in S1
3. Execute NOTIFY test_background, '1';select pg_background_detach(pg_background_launch('NOTIFY test_background, ''2'';')); in S2
4. Execute SELECT; in S1

Expected result: two notification messages with payloads 1 and 2 in S1.
Actual result: single notification message with payload 1.

Looks like pg_background_detach terminates pg_background_launch call (with rollback). Inserting pg_sleep(0.1) between pg_background_launch and pg_background_detach solves the problem.

PostgreSQL version: "PostgreSQL 9.6.3 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-11), 64-bit"

[rjuju]

Hi,

As far as I can see this is the same problem as reported in #1, as the logs show:

2021-05-16 23:04:07.711 CST [27600] ERROR:  unable to map dynamic shared memory segment
2021-05-16 23:04:07.713 CST [26820] LOG:  background worker "pg_background" (PID 27600) exited with exit code 1

So until this problem is fixed, you can either avoid to call pg_background_detach(), or call instead pg_background_result()