Horton

Re: POC: make mxidoff 64 bits

Heikki Linnakangas <hlinnaka@iki.fi>

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From: Heikki Linnakangas <hlinnaka@iki.fi>
To: Maxim Orlov <orlovmg@gmail.com>
Cc: Alvaro Herrera <alvherre@alvh.no-ip.org>, Alexander Korotkov <aekorotkov@gmail.com>, wenhui qiu <qiuwenhuifx@gmail.com>, Postgres hackers <pgsql-hackers@lists.postgresql.org>, Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Date: 2025-11-26T15:50:25Z
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.

On 26/11/2025 17:23, Maxim Orlov wrote:
> On Tue, 25 Nov 2025 at 13:07, Heikki Linnakangas <hlinnaka@iki.fi 
> <mailto:hlinnaka@iki.fi>> wrote:
>> GetOldMultiXactIdSingleMember() currently asserts that the offset is
>> never zero, but it should try to do something sensible in that case
>> instead of just failing.
> 
> Correct me if I'm wrong, but we added the assertion that offsets are
> never 0, based on the idea that case #2 will never take place during an
> update. If this isn't the case, this assertion could be removed.
> The rest of the function appears to work correctly.
> 
> I even think that, as an experiment, we could randomly reset some of the
> offsets to zero and nothing would happen, except that some data would
> be lost.

+1

> The most sensible thing we can do is give the user a warning, right?
> Something like, "During the update, we encountered some weird offset
> that shouldn't have been there, but there's nothing we can do about it,
> just take note."

Yep, makes sense.

- Heikki