Horton

Re: POC: enable logical decoding when wal_level = 'replica' without a server restart

Masahiko Sawada <sawada.mshk@gmail.com>

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From: Masahiko Sawada <sawada.mshk@gmail.com>
To: vignesh C <vignesh21@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, shveta malik <shveta.malik@gmail.com>, Peter Smith <smithpb2250@gmail.com>, "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>, Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>, Shlok Kyal <shlok.kyal.oss@gmail.com>, Bertrand Drouvot <bertranddrouvot.pg@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2025-12-02T16:00:08Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Fix regression test failure when wal_level is set to minimal.

  2. Toggle logical decoding dynamically based on logical slot presence.

  3. Disallow server start with sync_replication_slots = on and wal_level < logical.

On Tue, Dec 2, 2025 at 2:53 AM vignesh C <vignesh21@gmail.com> wrote:
>
> On Mon, 1 Dec 2025 at 12:33, Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> >
> > On Mon, Dec 1, 2025 at 12:20 AM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> >
> > I've attached the patch. All the comments I got so far have been
> > addressed in this version unless I'm missing something.
>
> Few comments:
> 1) We have an invalidation test at 044_invalidate_inactive_slots.pl
> which does an equivalent of this, I felt this can be removed and just
> the test_wal_level can be done from 044_invalidate_inactive_slots:

While 044_invalidate_inactive_slots.pl is not executed without
injection points, the test in 050_effective_wal_level.pl should be
doable without injection points. If we remove the test from
050_effective_wal_level.pl, we cannot cover the corresponding path
without injection points.

> 2) What are we verifying here, as a logical replication slot can be
> created without promotion too:
> # Confirm if we can create a logical slot after the promotion.
> $standby1->safe_psql('postgres',
> qq[select pg_create_logical_replication_slot('standby1_slot2', 'pgoutput')]
> );
>
> If it is not required we can remove it.

I think that this test case verifies that logical decoding is enabled
at the end of recovery (i.e., promotion) and we can create a logical
replication slot.

>
> 3) This message seems wrong:
> +       "cannot server with wal_level='minimal' as there is in-use
> logical slot");
> +
> +my $logfile = slurp_file($primary->logfile());
>
> Should it be:
> cannot start server with wal_level='minimal'

Agreed. Fixed in the next version patch.

Regards,

-- 
Masahiko Sawada
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