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From: shveta malik <shveta.malik@gmail.com>
Date: Tue, 10 Mar 2026 12:24:59 +0530
Message-ID: 
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Subject: Re: [PATCH] Add max_logical_replication_slots GUC
To: Fujii Masao <masao.fujii@gmail.com>
Cc: Ahmed Et-tanany <ahmed.ettanany@aiven.io>,
 =?UTF-8?Q?=C3=81lvaro_Herrera?= <alvherre@kurilemu.de>,
	pgsql-hackers@lists.postgresql.org, shveta malik <shveta.malik@gmail.com>
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On Thu, Jan 29, 2026 at 5:10=E2=80=AFPM Fujii Masao <masao.fujii@gmail.com>=
 wrote:
>
> On Wed, Jan 28, 2026 at 10:02=E2=80=AFPM Ahmed Et-tanany
> <ahmed.ettanany@aiven.io> wrote:
> >
> > Yes, that's what I meant.
>
> Would something like max_logical_wal_senders also be needed for your purp=
ose?
> Otherwise, logical replication connections could exhaust max_wal_senders =
and
> prevent physical replication connections from being established.
>

I could be mistaken, but I haven=E2=80=99t found a way to start a logical
replication stream without a replication slot. A replication
connection and walsender can exist without a slot, for example:
./psql "host=3Dlocalhost port=3D5432 user=3Duser1 dbname=3Dpostgres
replication=3Ddatabase"

However, converting that connection to logical replication requires a
slot from the max_logical_replication_slots pool. If that pool is
exhausted, the connection cannot be converted =E2=80=94 in which case,
wouldn=E2=80=99t a single GUC suffice?

I might be missing something =E2=80=94 are you referring to a different sce=
nario?
One possibility is if max_wal_senders is lower than
max_logical_replication_slots, which could exhaust WAL senders for
logical connections, though that would mostly be a configuration
issue. Isn't it?

thanks
Shveta