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From: Amit Kapila <amit.kapila16@gmail.com>
Date: Sat, 25 Feb 2023 16:00:05 +0530
Message-ID: <CAA4eK1+LRO7F-9RmsdhX044pZESMUsuynmB-eTzNOnhP65_S=w@mail.gmail.com>
Subject: Re: [PATCH] Use indexes on the subscriber when REPLICA IDENTITY is
 full on the publisher
To: =?UTF-8?B?w5ZuZGVyIEthbGFjxLE=?= <onderkalaci@gmail.com>
Cc: "shiy.fnst@fujitsu.com" <shiy.fnst@fujitsu.com>, Marco Slot <marco.slot@gmail.com>, 
	Tom Lane <tgl@sss.pgh.pa.us>, Andres Freund <andres@anarazel.de>, 
	"wangw.fnst@fujitsu.com" <wangw.fnst@fujitsu.com>, 
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
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On Tue, Feb 21, 2023 at 7:55 PM =C3=96nder Kalac=C4=B1 <onderkalaci@gmail.c=
om> wrote:
>
>>
>> I think this overhead seems to be mostly due to the need to perform
>> tuples_equal multiple times for duplicate values. I don't know if
>> there is any simple way to avoid this without using the planner stuff
>> as was used in the previous approach. So, this brings us to the
>> question of whether just providing a way to disable/enable the use of
>> index scan for such cases is sufficient or if we need any other way.
>>
>> Tom, Andres, or others, do you have any suggestions on how to move
>> forward with this patch?
>>
>
> Thanks for the feedback and testing. Due to personal circumstances,
> I could not reply the thread in the last 2 weeks, but I'll be more active
> going forward.
>
>  I also agree that we should have a way to control the behavior.
>
> I created another patch (v24_0001_optionally_disable_index.patch) which c=
an be applied
> on top of v23_0001_use_index_on_subs_when_pub_rep_ident_full.patch.
>
> The new patch adds a new subscription_parameter for both CREATE and ALTER=
 subscription
> named: enable_index_scan. The setting is valid only when REPLICA IDENTITY=
 is full.
>
> What do you think about such a patch to control the behavior? It does not=
 give a per-relation
> level of control, but still useful for many cases.
>

Wouldn't a table-level option like 'apply_index_scan' be better than a
subscription-level option with a default value as false? Anyway, the
bigger point is that we don't see a better way to proceed here than to
introduce some option to control this behavior.

I see this as a way to provide this feature for users but I would
prefer to proceed with this if we can get some more buy-in from senior
community members (at least one more committer) and some user(s) if
possible. So, I once again request others to chime in and share their
opinion.

--=20
With Regards,
Amit Kapila.