Thread

RE: How can end users know the cause of LR slot sync delays?

Zhijie Hou (Fujitsu) <houzj.fnst@fujitsu.com> — 2025-11-26T03:24:12Z

On Wednesday, November 26, 2025 11:00 AM Amit Kapila <amit.kapila16@gmail.com> wrote:
> 
> On Tue, Nov 25, 2025 at 5:18 PM Zhijie Hou (Fujitsu) <houzj.fnst@fujitsu.com>
> wrote:
> >
> > Here is the patch to modify the test.
> >
> 
> +##################################################
> +# Verify that slotsync skip statistics are correctly updated when the #
> +slotsync operation is skipped.
> +##################################################
> ....
> +$standby2->reload;
> +
> +# Commit the pending prepared transaction
> +$primary->safe_psql('postgres', "COMMIT PREPARED
> +'test_twophase_slotsync';");
> +$primary->wait_for_replay_catchup($standby2);
> +
> +# Remove all logical replication slots on the primary server to ensure
> +the # corresponding synced slots are also removed. This guarantees that
> +the safest # catalog_xmin on the standby is not preserved by existing
> +slots,
> allowing newly
> +# created slots to have a fresher initial catalog_xmin.
> +$primary->psql('postgres', qq(
> + SELECT pg_drop_replication_slot('lsub1_slot');
> + SELECT pg_drop_replication_slot('snap_test_slot');
> +));
> +
> +$subscriber2->safe_psql(
> + 'postgres', 'DROP SUBSCRIPTION regress_mysub2;');
> +
> +$standby2->safe_psql('postgres', "SELECT
> +pg_sync_replication_slots();");
> +
> +is( $standby2->safe_psql(
> + 'postgres',
> + q{SELECT count(*) = 0 FROM pg_replication_slots WHERE slot_name IN
> ('lsub1_slot', 'lsub2_slot', 'snap_test_slot');}
> + ),
> + "t",
> + 'synchronized slot has been dropped');
> 
> This is too much dependency of previous tests on the new one. We should do
> cleanup of previous tests separately, if we want to use some existing set up.
> Also, do we need to ensure that standby2's slots are dropped? Did we ever
> sync slots on standby2? If so, cleaning up here looks odd. This is to make new
> tests rely less on the outcome of previous tests.

I think we did not sync slots to standby2, so I removed the checks for that.

I also adjusted the test in a way that it cleans up existing slots before starting
new tests.

Here is the updated version.

Best Regards,
Hou zj