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: 2025-11-25T10:07:27Z
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.

Looking at the upgrade code, in light of the "IPC/MultixactCreation on 
the Standby server" thread [1], I think we need to make it more 
tolerant. It's possible that there are 0 offsets in 
pg_multixact/offsets. That might or might not be a problem: it's OK as 
long as those multixids don't appear in any heap table, or you might 
actually have lost those multixids, which is bad but the damage has 
already been done and upgrade should not get stuck on it. 
GetOldMultiXactIdSingleMember() currently asserts that the offset is 
never zero, but it should try to do something sensible in that case 
instead of just failing.

[1] 
https://www.postgresql.org/message-id/172e5723-d65f-4eec-b512-14beacb326ce%40yandex.ru

- Heikki