Horton

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

shveta malik <shveta.malik@gmail.com>

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From: shveta malik <shveta.malik@gmail.com>
To: Masahiko Sawada <sawada.mshk@gmail.com>
Cc: Amit Kapila <amit.kapila16@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>, shveta malik <shveta.malik@gmail.com>
Date: 2025-10-23T08:12:43Z
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 Thu, Oct 23, 2025 at 2:53 AM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>
> On Wed, Oct 22, 2025 at 4:06 AM shveta malik <shveta.malik@gmail.com> wrote:
> >
> > On Wed, Oct 22, 2025 at 2:58 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> > >
> > > On Wed, Oct 22, 2025 at 2:40 PM shveta malik <shveta.malik@gmail.com> wrote:
> > > >
> > > > On Fri, Oct 17, 2025 at 11:09 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> > > > >
> > > >
> > > > I want to discuss the create-publication case, which currently gives
> > > > this warning:
> > > >
> > > > postgres=# create publication pub1 for all tables;
> > > > WARNING:  logical decoding should be allowed to publish logical changes
> > > > HINT:  Before creating subscriptions, set "wal_level" >= "logical" or
> > > > create a logical replication slot when "wal_level" = "replica".
> > > > CREATE PUBLICATION
> > > >
> > > > But is this warning really necessary during publication creation?
> > > >
> > >
> > > On HEAD, the WARNING/HINT is as follows for the above case:
> > > WARNING:  "wal_level" is insufficient to publish logical changes
> > > HINT:  Set "wal_level" to "logical" before creating subscriptions.
> > >
> > > Shouldn't we simply change the HINT to "Set "wal_level" to "logical"
> > > or create a logical replication slot before creating subscriptions."?
> > >
> >
> > My point was do we really need this WARNING considering case a) does
> > not need it now and case b) also gives different ERROR (cases
> > mentioned in previous email). But if we plan to retain the WARNING,
> > then I agree with the change proposed here, it looks simpler and
> > better.
>
> I guess I understand your point. Without the patch, the WARNING
> message makes sense because if users create a publication with
> wal_level='replica', they need to change wal_level to 'logical' to
> start logical replication. That is, it works like telling users some
> required operations that they might have missed. On the other hand,
> with the patch, logical decoding is automatically enabled when they
> start logical replication, and any additional step is no longer
> necessary.

Right.

> I find the message makes less sense now but is still
> required in 'minimal' WAL level cases?
>

Yes, it is needed in 'minimal' wal-level case. We shall change the
check in CreatePublication() then.

thanks
Shveta