Re: Synchronizing slots from primary to standby

From: Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
To: shveta malik <shveta(dot)malik(at)gmail(dot)com>
Cc: Peter Smith <smithpb2250(at)gmail(dot)com>, "Hayato Kuroda (Fujitsu)" <kuroda(dot)hayato(at)fujitsu(dot)com>, "Drouvot, Bertrand" <bertranddrouvot(dot)pg(at)gmail(dot)com>, Bharath Rupireddy <bharath(dot)rupireddyforpostgres(at)gmail(dot)com>, Peter Eisentraut <peter(dot)eisentraut(at)enterprisedb(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Ashutosh Sharma <ashu(dot)coek88(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, Ajin Cherian <itsajin(at)gmail(dot)com>, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>
Subject: Re: Synchronizing slots from primary to standby
Date: 2023-09-22 10:18:43
Message-ID: CAA4eK1L3vTXcg-vV9HvahMRdTpDa6bEwb=YX4WvFYgJQ+uEunw@mail.gmail.com
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On Thu, Sep 21, 2023 at 9:16 AM shveta malik <shveta(dot)malik(at)gmail(dot)com> wrote:
>
> On Tue, Sep 19, 2023 at 10:29 AM shveta malik <shveta(dot)malik(at)gmail(dot)com> wrote:
>
> Currently in patch001, synchronize_slot_names is a GUC on both primary
> and physical standby. This GUC tells which all logical slots need to
> be synced on physical standbys from the primary. Ideally it should be
> a GUC on physical standby alone and each physical standby should be
> able to communicate the value to the primary (considering the value
> may vary for different physical replicas of the same primary). The
> primary on the other hand should be able to take UNION of these values
> and let the logical walsenders (belonging to the slots in UNION
> synchronize_slots_names) wait for physical standbys for confirmation
> before sending those changes to logical subscribers. The intent is
> logical subscribers should never be ahead of physical standbys.
>

Before getting into the details of 'synchronize_slot_names', I would
like to know whether we really need the second GUC
'standby_slot_names'. Can't we simply allow all the logical wal
senders corresponding to 'synchronize_slot_names' to wait for just the
physical standby(s) (physical slot corresponding to such physical
standby) that have sent ' synchronize_slot_names'list? We should have
one physical standby slot corresponding to one physical standby.

--
With Regards,
Amit Kapila.

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