Re: Synchronizing slots from primary to standby

From: Bertrand Drouvot <bertranddrouvot(dot)pg(at)gmail(dot)com>
To: Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
Cc: "Zhijie Hou (Fujitsu)" <houzj(dot)fnst(at)fujitsu(dot)com>, shveta malik <shveta(dot)malik(at)gmail(dot)com>, Ajin Cherian <itsajin(at)gmail(dot)com>, Peter Smith <smithpb2250(at)gmail(dot)com>, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Dilip Kumar <dilipbalaut(at)gmail(dot)com>, Nisha Moond <nisha(dot)moond412(at)gmail(dot)com>, "Hayato Kuroda (Fujitsu)" <kuroda(dot)hayato(at)fujitsu(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>, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>
Subject: Re: Synchronizing slots from primary to standby
Date: 2024-03-28 12:37:00
Message-ID: ZgVkbJBSI7Tqp78E@ip-10-97-1-34.eu-west-3.compute.internal
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Hi,

On Thu, Mar 28, 2024 at 05:05:35PM +0530, Amit Kapila wrote:
> On Thu, Mar 28, 2024 at 3:34 PM Bertrand Drouvot
> <bertranddrouvot(dot)pg(at)gmail(dot)com> wrote:
> >
> > On Thu, Mar 28, 2024 at 04:38:19AM +0000, Zhijie Hou (Fujitsu) wrote:
> >
> > > To fix this, we could use the fast forward logical decoding to advance the synced
> > > slot's lsn/xmin when syncing these values instead of directly updating the
> > > slot's info. This way, the snapshot will be serialized to disk when decoding.
> > > If we could not reach to the consistent point at the remote restart_lsn, the
> > > slot is marked as temp and will be persisted once it reaches the consistent
> > > point. I am still analyzing the fix and will share once ready.
> >
> > Thanks! I'm wondering about the performance impact (even in fast_forward mode),
> > might be worth to keep an eye on it.
> >
>
> True, we can consider performance but correctness should be a
> priority,

Yeah of course.

> and can we think of a better way to fix this issue?

I'll keep you posted if there is one that I can think of.

> > Should we create a 17 open item [1]?
> >
> > [1]: https://wiki.postgresql.org/wiki/PostgreSQL_17_Open_Items
> >
>
> Yes, we can do that.

done.

Regards,

--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com

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