Horton

Re: POC: make mxidoff 64 bits

wenhui qiu <qiuwenhuifx@gmail.com>

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From: wenhui qiu <qiuwenhuifx@gmail.com>
To: Heikki Linnakangas <hlinnaka@iki.fi>
Cc: Maxim Orlov <orlovmg@gmail.com>, Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>, Alvaro Herrera <alvherre@alvh.no-ip.org>, Alexander Korotkov <aekorotkov@gmail.com>, Postgres hackers <pgsql-hackers@lists.postgresql.org>
Date: 2025-11-18T01:47:45Z
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. Fix partial read handling in pg_upgrade's multixact conversion

  2. Increase timeout in multixid_conversion upgrade test

  3. Improve sanity checks on multixid members length

  4. Clarify comment on multixid offset wraparound check

  5. Never store 0 as the nextMXact

  6. Add runtime checks for bogus multixact offsets

  7. Widen MultiXactOffset to 64 bits

  8. Move pg_multixact SLRU page format definitions to a separate header

  9. Convert confusing macros in multixact.c to static inline functions

  10. Index SLRUs by 64-bit integers rather than by 32-bit integers

  11. Cope with possible failure of the oldest MultiXact to exist.

Hi Heikki
> I don't think we need to support that case. I hope there are no clusters
> in that state still in the wild, and you can work around it by upgrading
> to 9.3.5 or above and letting autovacuum run. But I wonder if a
> pre-upgrade check with a better error message would still be worthwhile.
I think we believe it is now highly unlikely to find instances of version
9.3; all users are advised to upgrade to the latest version first.




Thanks

On Tue, Nov 18, 2025 at 12:35 AM Heikki Linnakangas <hlinnaka@iki.fi> wrote:

> Here's yet another patch version. I spent the day reviewing this in
> detail and doing little cleanups here and there. I squashed the commits
> and wrote a proper commit message.
>
> One noteworthy refactoring is in pg_upgrade.c, to make it more clear (to
> me at least) how upgrade from version 9.2 and below now works. It was
> actually broken when I tested it. Not sure if I had broken it earlier or
> if it never worked, but in any case it works now.
>
> I also tested upgrading a cluster from an old minor version, < 9.3.5,
> where the control file has a bogus oldestMultiXid==1 value (see commit
> b6a3444fa6). As expected, you get a "could not open file" error:
>
> > Performing Upgrade
> > ------------------
> > Setting locale and encoding for new cluster                   ok
> > ...
> > Deleting files from new pg_multixact/members                  ok
> > Deleting files from new pg_multixact/offsets                  ok
> > Converting pg_multixact files
> > could not open file
> "/home/heikki/pgsql.93stable/data/pg_multixact/offsets/0000": No such file
> or directory
> > Failure, exiting
>
> I don't think we need to support that case. I hope there are no clusters
> in that state still in the wild, and you can work around it by upgrading
> to 9.3.5 or above and letting autovacuum run. But I wonder if a
> pre-upgrade check with a better error message would still be worthwhile.
>
>
> Ashutosh, you were interested in reviewing this earlier. Would you have
> a chance to review this now, before I commit it? Alexander, Alvaro,
> would you have a chance to take a final look too, please?
>
> - Heikki
>