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help / color / mirror / Atom feedFrom: Bertrand Drouvot <[email protected]>
To: shveta malik <[email protected]>
Cc: Amit Kapila <[email protected]>
Cc: Masahiko Sawada <[email protected]>
Cc: Zhijie Hou (Fujitsu) <[email protected]>
Cc: Dilip Kumar <[email protected]>
Cc: Peter Smith <[email protected]>
Cc: Nisha Moond <[email protected]>
Cc: Hayato Kuroda (Fujitsu) <[email protected]>
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Cc: Peter Eisentraut <[email protected]>
Cc: Bruce Momjian <[email protected]>
Cc: Ashutosh Sharma <[email protected]>
Cc: Andres Freund <[email protected]>
Cc: pgsql-hackers <[email protected]>
Cc: Ajin Cherian <[email protected]>
Cc: Alvaro Herrera <[email protected]>
Subject: Re: Synchronizing slots from primary to standby
Date: Fri, 19 Jan 2024 08:12:33 +0000
Message-ID: <[email protected]> (raw)
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Hi,
On Fri, Jan 19, 2024 at 11:46:51AM +0530, shveta malik wrote:
> On Fri, Jan 19, 2024 at 11:23 AM Amit Kapila <[email protected]> wrote:
> >
> > > > 5 === (coming from v62-0002)
> > > > + Assert(tuplestore_tuple_count(res->tuplestore) == 1);
> > > >
> > > > Is it even possible for the related query to not return only one row? (I think the
> > > > "count" ensures it).
> > >
> > > I think you are right. This assertion was added sometime back on the
> > > basis of feedback on hackers. Let me review that again. I can consider
> > > this comment in the next version.
> > >
> >
> > OTOH, can't we keep the assert as it is but remove "= 1" from
> > "count(*) = 1" in the query. There shouldn't be more than one slot
> > with same name on the primary. Or, am I missing something?
>
> There will be 1 record max and 0 record if the primary_slot_name is
> invalid.
I think we'd have exactly one record in all the cases (due to the count):
postgres=# SELECT pg_is_in_recovery(), count(*) FROM pg_replication_slots WHERE 1 = 2;
pg_is_in_recovery | count
-------------------+-------
f | 0
(1 row)
postgres=# SELECT pg_is_in_recovery(), count(*) FROM pg_replication_slots WHERE 1 = 1;
pg_is_in_recovery | count
-------------------+-------
f | 1
(1 row)
> Keeping 'count(*)=1' gives the benefit that it will straight
> away give us true/false indicating if we are good or not wrt
> primary_slot_name. I feel Assert can be removed and we can simply
> have:
>
> if (!tuplestore_gettupleslot(res->tuplestore, true, false, tupslot))
> elog(ERROR, "failed to fetch primary_slot_name tuple");
>
I'd also vote for keeping it as it is and remove the Assert.
Regards,
--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com
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Subject: Re: Synchronizing slots from primary to standby
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