Horton

Re: Slow catchup of 2PC (twophase) transactions on replica in LR

Ajin Cherian <itsajin@gmail.com>

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From: Ajin Cherian <itsajin@gmail.com>
To: Давыдов Виталий <v.davydov@postgrespro.ru>
Cc: Heikki Linnakangas <hlinnaka@iki.fi>, pgsql-hackers@lists.postgresql.org
Date: 2024-04-04T05:23:15Z
Lists: pgsql-hackers

Commits

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  1. Fix random failure in 021_twophase.

  2. Allow altering of two_phase option of a SUBSCRIPTION.

  3. Doc: use true|false rather than on|off for "failover" option

  4. Support an optional asynchronous commit mode, in which we don't flush WAL

Attachments

On Wed, Mar 6, 2024 at 1:29 AM Давыдов Виталий <v.davydov@postgrespro.ru>
wrote:

> In usual work, the subscription has two_phase = on. I have to change this
> option at catchup stage only, but this parameter can not be altered. There
> 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
> = off will not work.
>
>
>
The altering of two_phase was restricted because if there was a previously
prepared transaction on the subscriber when the two_phase was on, and then
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.

Thanks to Kuroda-san for working on the patch.

regards,
Ajin Cherian
Fujitsu Australia