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Re: cleanup patches for incremental backup

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Nathan Bossart <nathandbossart@gmail.com>
Cc: Alexander Lakhin <exclusion@gmail.com>, Matthias van de Meent <boekewurm+postgres@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2024-01-29T20:18:50Z
Lists: 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

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Avoid overflow in MaybeRemoveOldWalSummaries().

  2. Revert "Temporary patch to help debug pg_walsummary test failures."

  3. Revise pg_walsummary's 002_blocks test to avoid spurious failures.

  4. Temporary patch to help debug pg_walsummary test failures.

  5. More documentation updates for incremental backup.

  6. Fix typos.

  7. Fix typo.

  8. Try to fix pg_walsummary buildfarm failures.

  9. Repair various defects in dc212340058b4e7ecfc5a7a81ec50e7a207bf288.

  10. Add new pg_walsummary tool.

  11. Add new function pg_get_wal_summarizer_state().

  12. Document WAL summarization information functions.