Re: pgsql: Wait for WAL summarization to catch up before creating .partial

On Fri, Jul 26, 2024 at 10:01 PM Robert Haas <rhaas(at)postgresql(dot)org> wrote:
> Wait for WAL summarization to catch up before creating .partial file.
>
> When a standby is promoted, CleanupAfterArchiveRecovery() may decide
> to rename the final WAL file from the old timeline by adding ".partial"
> to the name. If WAL summarization is enabled and this file is renamed
> before its partial contents are summarized, WAL summarization breaks:
> the summarizer gets stuck at that point in the WAL stream and just
> errors out.
>
> To fix that, first make the startup process wait for WAL summarization
> to catch up before renaming the file. Generally, this should be quick,
> and if it's not, the user can shut off summarize_wal and try again.
> To make this fix work, also teach the WAL summarizer that after a
> promotion has occurred, no more WAL can appear on the previous
> timeline: previously, the WAL summarizer wouldn't switch to the new
> timeline until we actually started writing WAL there, but that meant
> that when the startup process was waiting for the WAL summarizer, it
> was waiting for an action that the summarizer wasn't yet prepared to
> take.
>
> In the process of fixing these bugs, I realized that the logic to wait
> for WAL summarization to catch up was spread out in a way that made
> it difficult to reuse properly, so this code refactors things to make
> it easier.
>
> Finally, add a test case that would have caught this bug and the
> previously-fixed bug that WAL summarization sometimes needs to back up
> when the timeline changes.

It appears that I was late with my review [1]. But the new tap test
could still use pgperltidy.

Links.
1. https://www.postgresql.org/message-id/CAPpHfduW3du0W%3D3noztdaJ6evGP9gqT1AGk_rwXrqDyus1zZoQ%40mail.gmail.com

------
Regards,
Alexander Korotkov
Supabase