Re: [PATCH] Use indexes on the subscriber when REPLICA IDENTITY is full on the publisher

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From: Dilip Kumar <[email protected]>
To: Amit Kapila <[email protected]>
Cc: Önder Kalacı <[email protected]>
Cc: [email protected] <[email protected]>
Cc: [email protected] <[email protected]>
Cc: [email protected] <[email protected]>
Cc: Marco Slot <[email protected]>
Cc: Tom Lane <[email protected]>
Cc: Andres Freund <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Subject: Re: [PATCH] Use indexes on the subscriber when REPLICA IDENTITY is full on the publisher
Date: Mon, 6 Mar 2023 19:25:37 +0530
Message-ID: <CAFiTN-vjFKTB7uWSkC0_J1NkfwyaFz+6TzW9bf2GS1XM7YSQ8g@mail.gmail.com> (raw)
In-Reply-To: <CAA4eK1Lt8MCEpwbgq623ySaquz5sNoMk1SVAQ8XN-QDxRa5E9A@mail.gmail.com>
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On Mon, Mar 6, 2023 at 4:45 PM Amit Kapila <[email protected]> wrote:
>
> On Mon, Mar 6, 2023 at 4:18 PM Dilip Kumar <[email protected]> wrote:
> >
> > On Mon, Mar 6, 2023 at 2:38 PM Önder Kalacı <[email protected]> wrote:
> > >
> > I was going through the thread and patch,  I noticed that in the
> > initial version, we were depending upon the planner to let it decide
> > whether index scan is cheaper or not and which index to pick.  But in
> > the latest patch if a useful index exists then we chose that without
> > comparing the cost of whether it is cheaper than sequential scan or
> > not.  Is my understanding correct?  What is the reason for the same,
> >
>
> Yes, your understanding is correct. The main reason is that we don't
> have an agreement on using the internal planner APIs for apply. That
> will be a long-term maintenance burden. See discussion around email
> [1]. So, we decided to use the current infrastructure to achieve index
> scans during apply when publisher has replica identity full. This will
> still be win in many cases and we are planning to provide a knob to
> disable this feature.
>
> [1] - https://www.postgresql.org/message-id/3466340.1673117404%40sss.pgh.pa.us

Okay, this makes sense, so basically, in "replica identify full" case
instead of doing the default sequence scan we will provide a knob to
either choose index scan or sequence scan, and that seems reasonable
to me.

-- 
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com

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