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From: Amit Kapila <amit.kapila16@gmail.com>
Date: Thu, 4 Apr 2024 11:07:49 +0530
Message-ID: <CAA4eK1+n7M2S1OpoGWDd+YZkDCuURMdVRbvP0eELQUvWgmDneg@mail.gmail.com>
Subject: Re: Slow catchup of 2PC (twophase) transactions on replica in LR
To: Ajin Cherian <itsajin@gmail.com>
Cc: =?UTF-8?B?0JTQsNCy0YvQtNC+0LIg0JLQuNGC0LDQu9C40Lk=?= <v.davydov@postgrespro.ru>, 
	Heikki Linnakangas <hlinnaka@iki.fi>, pgsql-hackers@lists.postgresql.org
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On Thu, Apr 4, 2024 at 10:53=E2=80=AFAM Ajin Cherian <itsajin@gmail.com> wr=
ote:
>
> On Wed, Mar 6, 2024 at 1:29=E2=80=AFAM =D0=94=D0=B0=D0=B2=D1=8B=D0=B4=D0=
=BE=D0=B2 =D0=92=D0=B8=D1=82=D0=B0=D0=BB=D0=B8=D0=B9 <v.davydov@postgrespro=
.ru> wrote:
>>
>> In usual work, the subscription has two_phase =3D on. I have to change t=
his option at catchup stage only, but this parameter can not be altered. Th=
ere was a patch proposal in past to implement altering of two_phase option,=
 but it was rejected. I think, the recreation of the subscription with two_=
phase =3D off will not work.
>>
>>
>
> The altering of two_phase was restricted because if there was a previousl=
y prepared transaction on the subscriber when the two_phase was on, and the=
n it was turned off, the apply worker on the subscriber would re-apply the =
transaction a second time and this might result in an inconsistent replica.
> Here's a patch that allows toggling two_phase option provided that there =
are no pending uncommitted prepared transactions on the subscriber for that=
 subscription.
>

I think this would probably be better than the current situation but
can we think of a solution to allow toggling the value of two_phase
even when prepared transactions are present? Can you please summarize
the reason for the problems in doing that and the solutions, if any?

--=20
With Regards,
Amit Kapila.