Re: Exit walsender before confirming remote flush in logical replication

Hello Fujii-san,

06.04.2026 18:32, Andres Freund wrote:
> Hi,
>
> On 2026-04-06 11:40:24 +0900, Fujii Masao wrote:
>> I've pushed the patch. Thanks!
> Failed on CI just now:
>
> https://cirrus-ci.com/task/6745359004729344?logs=test_world#L410
> https://api.cirrus-ci.com/v1/artifact/task/6745359004729344/testrun/build/testrun/subscription/038_walsnd_shutdown_timeout/log/regress_log_038_walsnd_shutdown_timeout

A recent failure occurred on the buildfarm [1] indicates another stability
issue, this time with the test itself, I guess:
[21:12:03.301](0.068s) ok 3 - have walreceiver pid 2275585
### Stopping node "publisher" using mode fast
# Running: pg_ctl --pgdata 
/home/bf/bf-build/tamandua/HEAD/pgsql.build/testrun/subscription/038_walsnd_shutdown_timeout/data/t_038_walsnd_shutdown_timeout_publisher_data/pgdata 
--mode fast stop
waiting for server to shut down.... done
server stopped
# No postmaster PID for node "publisher"
[21:12:03.752](0.452s) not ok 4 - walsender exits due to wal_sender_shutdown_timeout even when both physical and logical 
replication are stalled
[21:12:03.753](0.001s) #   Failed test 'walsender exits due to wal_sender_shutdown_timeout even when both physical and 
logical replication are stalled'
#   at /home/bf/bf-build/tamandua/HEAD/pgsql/src/test/subscription/t/038_walsnd_shutdown_timeout.pl line 189.
### Stopping node "subscriber" using mode fast

038_walsnd_shutdown_timeout_subscriber.log doesn't really contain the
expected warning:
2026-05-29 21:11:58.777 CEST [2273817][logical replication apply worker][124/2:0] LOG:  logical replication apply worker 
for subscription "test_sub" has started
2026-05-29 21:12:03.232 CEST [2271870][client backend][4/6:0] LOG: statement: BEGIN;
2026-05-29 21:12:03.232 CEST [2271870][client backend][4/6:0] LOG: statement: LOCK TABLE test_tab IN EXCLUSIVE MODE;
2026-05-29 21:12:03.232 CEST [2271870][client backend][4/6:0] LOG: statement: ;
2026-05-29 21:12:03.268 CEST [2273817][logical replication apply worker][124/0:0] LOG:  received message via 
replication: WARNING: replication slot "test_slot" specified in parameter "synchronized_standby_slots" does not have 
active_pid
     DETAIL:  Logical replication is waiting on the standby associated with replication slot "test_slot".
     HINT:  Start the standby associated with the replication slot "test_slot", or amend parameter 
"synchronized_standby_slots".
2026-05-29 21:12:03.433 CEST [2273817][logical replication apply worker][124/0:0] ERROR:  could not receive data from 
WAL stream: ERROR:  replication slot "test_slot" specified in parameter "synchronized_standby_slots" does not have 
active_pid
     DETAIL:  Logical replication is waiting on the standby associated with replication slot "test_slot".
     HINT:  Start the standby associated with the replication slot "test_slot", or amend parameter 
"synchronized_standby_slots".
2026-05-29 21:12:03.437 CEST [2271017][postmaster][:0] LOG: background worker "logical replication apply worker" (PID 
2273817) exited with exit code 1
2026-05-29 21:12:03.439 CEST [2275785][logical replication apply worker][125/2:0] LOG:  logical replication apply worker 
for subscription "test_sub" has started
2026-05-29 21:12:03.441 CEST [2275785][logical replication apply worker][125/0:0] ERROR:  apply worker for subscription 
"test_sub" could not connect to the publisher: connection to server on socket "/tmp/3gDgOpAsXL/.s.PGSQL.27739" failed: 
FATAL:  the database system is shutting down
2026-05-29 21:12:03.445 CEST [2271017][postmaster][:0] LOG: background worker "logical replication apply worker" (PID 
2275785) exited with exit code 1
2026-05-29 21:12:03.763 CEST [2271870][client backend][:0] LOG: disconnection: session time: 0:00:08.180 user=bf 
database=postgres host=[local]
2026-05-29 21:12:03.767 CEST [2271017][postmaster][:0] LOG: received fast shutdown request

I think this can be explained by the fact that walrcv->ready_to_display
is set before WalReceiverMain's loop reached. I've reproduced this test
failure with:
--- a/src/backend/replication/walreceiver.c
+++ b/src/backend/replication/walreceiver.c
@@ -280,6 +280,7 @@ WalReceiverMain(const void *startup_data, size_t startup_data_len)
      walrcv->sender_port = 0;
      walrcv->ready_to_display = true;
      SpinLockRelease(&walrcv->mutex);
+pg_usleep(500 * 1000);

      /* Establish the connection to the primary for XLOG streaming */
      appname = cluster_name[0] ? cluster_name : "walreceiver";


Could you please look if this can be improved?

[1] https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=tamandua&dt=2026-05-29%2019%3A03%3A21

Best regards,
Alexander