Re: BUG #19488: Standby connection fails after dropping on login event trigger enabled always

Hi,

On Wed, 20 May 2026 at 17:35, Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:

> On Wed, May 20, 2026 at 8:31 PM Alexander Korotkov <aekorotkov(at)gmail(dot)com>
> wrote:
> >
> > On Wed, May 20, 2026 at 1:03 PM Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
> wrote:
> > > On Wed, May 20, 2026 at 1:37 PM Ayush Tiwari
> > > <ayushtiwari(dot)slg01(at)gmail(dot)com> wrote:
> > > > Thanks for the report and the precise repro.
> > >
> > > +1
> > >
> > > > Attached patch adds a RecoveryInProgress() check to skip the cleanup
> > > > branch on standbys.
> > >
> > > Thanks for investigating this issue and for the patch!
> > > The patch looks good to me.
> > >
> > > > I think this needs to be backpatched too.
> > >
> > > Yes. Seems this should be backpatched to v17, where login event
> triggers
> > > were introduced.
> >
> > I've added a tap test reproducing the bug. I'm going to push and
> > backpatch this to v17 if no objections.
>
> +# Wait for the standby to replay the CREATE/DROP catalog state. At
> +# this point the standby's pg_database.dathasloginevt is still true.
> +$primary->wait_for_replay_catchup($standby);
> +
> +# A new connection to the standby exercises EventTriggerOnLogin()'s
> +# cleanup branch. With the RecoveryInProgress() guard, that branch is
> +# skipped on the standby and the connection succeeds. Without it the
> +# session aborts with a FATAL about AccessExclusiveLock. Probing the
> +# flag itself via safe_psql is what triggers the cleanup path.
> +is( $standby->safe_psql(
> + 'postgres',
> + "SELECT dathasloginevt FROM pg_database WHERE datname = 'postgres'"),
> + 't',
> + 'standby accepts connection and reports dangling dathasloginevt');
>
> The test looks unstable to me. wait_for_replay_catchup() may connect to
> the primary to obtain the flush LSN, which could cause dathasloginevt to
> become false before the subsequent safe_psql() call on the standby.
>

I think Fuji-san is right, can we do something like this:

my $drop_lsn = $primary->safe_psql(
'postgres', q{
BEGIN;
DROP EVENT TRIGGER init_session;
DROP FUNCTION init_session();
COMMIT;
SELECT pg_current_wal_lsn();
});

$primary->wait_for_catchup($standby, 'replay', $drop_lsn);

Then the following standby connection should reliably exercise the case
where dathasloginevt is still true on the standby but no login event
trigger remains.

Regards,
Ayush