Horton

Re: Making pg_rewind faster

John H <johnhyvr@gmail.com>

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From: John H <johnhyvr@gmail.com>
To: Srinath Reddy Sadipiralla <srinath2133@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>, wenhui qiu <qiuwenhuifx@gmail.com>, Japin Li <japinli@hotmail.com>, Michael Paquier <michael@paquier.xyz>, Andres Freund <andres@anarazel.de>, Alexander Korotkov <aekorotkov@gmail.com>, Justin Kwan <justinpkwan@outlook.com>, Tom Lane <tgl@sss.pgh.pa.us>, pgsql-hackers <pgsql-hackers@postgresql.org>, vignesh <vignesh@cloudflare.com>, vignesh ravichandran <admin@viggy28.dev>, "hlinnaka@iki.fi" <hlinnaka@iki.fi>, "jkwan@cloudflare.com" <jkwan@cloudflare.com>
Date: 2025-10-09T21:48:33Z
Lists: pgsql-hackers

Commits

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

  1. pg_rewind: Skip copy of WAL segments generated before point of divergence

  2. pg_rewind: Extend code detecting relation files to work with WAL files

  3. Split TESTDIR into TESTLOGDIR and TESTDATADIR

Hey Srinath

On Thu, Oct 9, 2025 at 12:09 PM Srinath Reddy Sadipiralla
<srinath2133@gmail.com> wrote:
> ...
> 1) if the timeline switch happens in middle of segment ,copy data from the last WAL segment and create WAL file with same segno but different timelineID,in this case the starting WAL file for the new timeline will be 000000020000000000000003
> 2) if the timeline switch happens at segment boundary , just create next segment for this case the starting WAL file for the new timeline will be 000000020000000000000004
>
> so basically the files which exists in source and not in target like the new timeline WAL segments will be copied to target in total before we reach decide_wal_file_action , so i think we don't need to think about copying WAL files after divergence point by calculating and checking against last_common_segno which we are doing in our current approach , i think we can just do
>
> ...

That's a great point. I need to think about it some more but the
reasoning makes sense to me.
I think 'last_common_segno ' is only useful as another sanity check
but we already have the size
ones.

Thanks,

-- 
John Hsu - Amazon Web Services