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

On Tue, Apr 16, 2024 at 7:48 AM Hayato Kuroda (Fujitsu)
<kuroda(dot)hayato(at)fujitsu(dot)com> wrote:
>
> > > FYI - We also considered the idea which walsender waits until all prepared
> > transactions
> > > are resolved before decoding and sending changes, but it did not work well
> > > - the restarted walsender sent only COMMIT PREPARED record for
> > transactions which
> > > have been prepared before disabling the subscription. This happened because
> > > 1) if the two_phase option of slots is false, the confirmed_flush can be ahead of
> > > PREPARE record, and
> > > 2) after the altering and restarting, start_decoding_at becomes same as
> > > confirmed_flush and records behind this won't be decoded.
> > >
> >
> > I don't understand the exact problem you are facing. IIUC, if the
> > commit is after start_decoding_at point and prepare was before it, we
> > expect to send the entire transaction followed by a commit record. The
> > restart_lsn should be before the start of such a transaction and we
> > should have recorded the changes in the reorder buffer.
>
> This behavior is right for two_phase = false case. But if the parameter is
> altered between PREPARE and COMMIT PREPARED, there is a possibility that only
> COMMIT PREPARED is sent.
>

Can you please once consider the idea shared by me at [1] (One naive
idea is that on the publisher .....) to solve this problem?

[1] - https://www.postgresql.org/message-id/CAA4eK1K1fSkeK%3Dkc26G5cq87vQG4%3D1qs_b%2Bno4%2Bep654SeBy1w%40mail.gmail.com

--
With Regards,
Amit Kapila.