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From: shveta malik <[email protected]>
To: Fujii Masao <[email protected]>
Cc: Ahmed Et-tanany <[email protected]>
Cc: Álvaro Herrera <[email protected]>
Cc: [email protected]
Cc: shveta malik <[email protected]>
Subject: Re: [PATCH] Add max_logical_replication_slots GUC
Date: Tue, 10 Mar 2026 12:24:59 +0530
Message-ID: <CAJpy0uC3aJzu_1zsaShL0UAy763MuJ3KOBZORb-a842NQ41tpg@mail.gmail.com> (raw)
In-Reply-To: <CAHGQGwEaBw9dd+Nzb2ETDJ-40nJTo6GRXrG_FcP0rmw3_-qU_Q@mail.gmail.com>
References: <CAD7nQBD1iy3NAS2YRDUH+zk0g=50px_h_wRsLcFkai7R_RF6VQ@mail.gmail.com>
	<[email protected]>
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	<CAHGQGwEaBw9dd+Nzb2ETDJ-40nJTo6GRXrG_FcP0rmw3_-qU_Q@mail.gmail.com>

On Thu, Jan 29, 2026 at 5:10 PM Fujii Masao <[email protected]> wrote:
>
> On Wed, Jan 28, 2026 at 10:02 PM Ahmed Et-tanany
> <[email protected]> wrote:
> >
> > Yes, that's what I meant.
>
> Would something like max_logical_wal_senders also be needed for your purpose?
> Otherwise, logical replication connections could exhaust max_wal_senders and
> prevent physical replication connections from being established.
>

I could be mistaken, but I haven’t 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=localhost port=5432 user=user1 dbname=postgres
replication=database"

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 — in which case,
wouldn’t a single GUC suffice?

I might be missing something — are you referring to a different scenario?
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

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