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From: Masahiko Sawada <sawada.mshk@gmail.com>
Date: Wed, 22 Apr 2026 10:01:01 -0700
Message-ID: 
 <CAD21AoD_m+Qr8fBnHAR50XFdoYACZHw=9xotmFrUGyDG4FhwVg@mail.gmail.com>
Subject: Re: Fix pg_upgrade to detect invalid logical replication slots on
 PG19
To: shveta malik <shveta.malik@gmail.com>
Cc: Lakshmi N <lakshmin.jhs@gmail.com>,
	"pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>
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On Wed, Apr 22, 2026 at 1:02=E2=80=AFAM Masahiko Sawada <sawada.mshk@gmail.=
com> wrote:
>
> On Tue, Apr 21, 2026 at 9:27=E2=80=AFPM shveta malik <shveta.malik@gmail.=
com> wrote:
> >
> > On Mon, Apr 20, 2026 at 2:28=E2=80=AFPM Lakshmi N <lakshmin.jhs@gmail.c=
om> wrote:
> > >
> > > Hi Hackers,
> > >
> > > The PG19-optimized slot catchup query uses a CTE that filters on
> > > invalidation_reason IS NULL, then cross-joins it with the main slot
> > > query.  When ALL logical slots in a database are invalid, the CTE
> > > returns zero rows, and the cross join produces an empty result set.
> > > This causes pg_upgrade to silently skip those slots entirely --
> > > neither detecting them as invalid (which should block the upgrade)
> > > nor attempting to migrate them.
> > >
> > > The pre-PG19 query path does not have this problem because it queries
> > > pg_replication_slots directly without a cross join. This may not impa=
ct
> > > upgrade to PG19 but will change the behavior for PG20 upgrade.
>
> Thank you for the report.
>
> > >
> > > Fix by changing the cross join to a LEFT JOIN,
> > > so that invalid slots still appear in the result set with NULL
> > > caught_up values.
> > >
> >
> > I agree with the problem here.
>
> I've confirmed the bug and the patch fixes it. The patch looks good to
> me, so I'm going to push it tomorrow barring any objections.

Pushed.

Regards,

--=20
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com