Horton

Re: POC: make mxidoff 64 bits

Maxim Orlov <orlovmg@gmail.com>

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From: Maxim Orlov <orlovmg@gmail.com>
To: Heikki Linnakangas <hlinnaka@iki.fi>
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: 2025-12-04T15:33:47Z
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.

Attachments

On Thu, 4 Dec 2025 at 13:39, Heikki Linnakangas <hlinnaka@iki.fi> wrote:

> However, that doesn't hold for pg_upgrade. pg_upgrade will try to read
> all the multixids. So we need to make the multixact reading code
> tolerant of the situations that could be present after a crash. I think
> the right philosophy here is that we try to read all the old multixids,
> and do our best to interpret them the same way that the old server
> would.


Something like attached?

Now previous scheme of upgrade with the bytes joggling start
looking not so bad. Just a funny thought that came to my mind.

Perhaps we should check that all the files exist and have the correct

sizes in the pre-check stage


Not sure about it. Because SLRU does not support "holes", simply
checking if the first and last multixacts exist will be enough. But
we'll do it anyway in a real conversion.

PFA to start a conversation.

-- 
Best regards,
Maxim Orlov.