Re: Slow catchup of 2PC (twophase) transactions on replica in LR

vignesh C <vignesh21@gmail.com>

From: vignesh C <vignesh21@gmail.com>

To: Amit Kapila <amit.kapila16@gmail.com>

Cc: Tom Lane <tgl@sss.pgh.pa.us>, Peter Smith <smithpb2250@gmail.com>, "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>, "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>, "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>, Vitaly Davydov <v.davydov@postgrespro.ru>, Ajin Cherian <itsajin@gmail.com>

Date: 2024-07-30T10:32:06Z

Lists: pgsql-hackers

Commits

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Fix random failure in 021_twophase.
- 0dcea330babd 18.0 landed
Allow altering of two_phase option of a SUBSCRIPTION.
- 1462aad2e447 18.0 landed
Doc: use true|false rather than on|off for "failover" option
- fa65a022db26 17.0 cited
Support an optional asynchronous commit mode, in which we don't flush WAL
- 4a78cdeb6b59 8.3.0 cited

Attachments

0001-Fix-random-failure-in-021_twophase.patch (text/x-patch) patch 0001
Reproduce_random_021_twophase_test_failure.patch (text/x-patch) patch

On Thu, 25 Jul 2024 at 08:39, Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Wed, Jul 24, 2024 at 9:13 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> >
> > Amit Kapila <amit.kapila16@gmail.com> writes:
> > > I merged these changes, made a few other cosmetic changes, and pushed the patch.
> >
> > There is a CF entry pointing at this thread [1].  Should it be closed?
> >
>
> Yes, closed now. Thanks for the reminder.

I noticed one random test failure in my environment with 021_twophase test.
[10:37:01.131](0.053s) ok 24 - should be no prepared transactions on subscriber
error running SQL: 'psql:<stdin>:2: ERROR:  cannot alter two_phase
when logical replication worker is still running
HINT:  Try again after some time.'

We can reproduce the issue by adding a delay at apply_worker_exit like
in the attached Reproduce_random_021_twophase_test_failure.patch
patch.

This is happening because the check here is wrong:
+$node_subscriber->poll_query_until('postgres',
+   "SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type =
'logical replication worker'"

Here "logical replication worker" should be "logical replication apply worker".

Attached patch has the changes for the same.

Regards,
Vignesh