| From: | Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> |
|---|---|
| To: | Tomas Vondra <tomas(at)vondra(dot)me> |
| Cc: | Ashutosh Bapat <ashutosh(dot)bapat(dot)oss(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: logical replication: restart_lsn can go backwards (and more), seems broken since 9.4 |
| Date: | 2024-11-12 06:32:18 |
| Message-ID: | CAD21AoA9nuyNhLT12hxe-U1rVgybQ+DZtGqFYM2BnLY-QGG3bA@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Mon, Nov 11, 2024 at 2:08 PM Tomas Vondra <tomas(at)vondra(dot)me> wrote:
>
>
> But neither of those fixes prevents backwards move for confirmed_flush
> LSN, as enforced by asserts in the 0005 patch. I don't know if this
> assert is incorrect or now. It seems natural that once we get a
> confirmation for some LSN, we can't move before that position, but I'm
> not sure about that. Maybe it's too strict.
Hmm, I'm concerned that it might be another problem. I think there are
some cases where a subscriber sends a flush position older than slot's
confirmed_flush as a feedback message. But it seems to be dangerous if
we always accept it as a new confirmed_flush value. It could happen
that confirm_flush could be set to a LSN older than restart_lsn.
Regards,
--
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com
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