Re: cleanup patches for incremental backup - Mailing list pgsql-hackers

From Robert Haas
Subject Re: cleanup patches for incremental backup
Date
Msg-id CA+Tgmob50yte0TN-vsR8ZL-CqxsEVNKrN1QNpo7z=hr3kxfTNQ@mail.gmail.com
Whole thread Raw
In response to Re: cleanup patches for incremental backup  (Nathan Bossart <nathandbossart@gmail.com>)
Responses Re: cleanup patches for incremental backup
List pgsql-hackers
On Mon, Jan 29, 2024 at 1:21 PM Nathan Bossart <nathandbossart@gmail.com> wrote:
> > Ah, I think this query:
> >
> >       SELECT tli, start_lsn, end_lsn from pg_available_wal_summaries()
> >               WHERE tli = $summarized_tli AND end_lsn > '$summarized_lsn'
> >
> > is returning more than one row in some cases.  I attached a quick sketch of
> > an easy way to reproduce the issue as well as one way to fix it.
>
> The buildfarm just caught a failure with the new logging in place:
>
>         https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=calliphoridae&dt=2024-01-29%2018%3A09%3A10
>
> I'm not totally sure my "fix" is correct, but I think this does confirm the
> theory.

Ah. The possibilities of ending up with TWO new WAL summaries never
occurred to me. Things that never occurred to the developer are a
leading cause of bugs, and so here.

I'm wondering if what we need to do is run pg_walsummary on both
summary files in that case. If we just pick one or the other, how do
we know which one to pick?

--
Robert Haas
EDB: http://www.enterprisedb.com



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