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Re: Fix bug in multixact Oldest*MXactId initialization and access

Sami Imseih <samimseih@gmail.com>

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From: Sami Imseih <samimseih@gmail.com>
To: Heikki Linnakangas <hlinnaka@iki.fi>
Cc: Chao Li <li.evan.chao@gmail.com>, Yura Sokolov <y.sokolov@postgrespro.ru>, "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>
Date: 2026-03-02T19:09:07Z
Lists: pgsql-hackers 
> > It says “Each is indexed by ProcNumber”, but it’s no longer accurate for OldestMemberMXactId prepared-xact entries, which now use index (procno - FIRST_PREPARED_XACT_PROC_NUMBER).
>
> Fixed those and some other comment work, and pushed. Thanks!
>

Thanks! what are your thoughts about adding a test like the one
here [1] ? This allows us to test correct handling of prepared
transaction dummy procs. The asserts added will not cover
this case.

What do you think?

[1] [https://www.postgresql.org/message-id/CAA5RZ0twq5bNMq0r0QNoopQnAEv%2BJ3qJNCrLs7HVqTEntBhJ%3Dg%40mail.gmail.com]

--
Sami Imseih
Amazon Web Services (AWS)

Commits

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

  1. Add test for row-locking and multixids with prepared transactions

  2. Skip prepared_xacts test if max_prepared_transactions < 2

  3. Fix OldestMemberMXactId and OldestVisibleMXactId array usage

  4. Redefine backend ID to be an index into the proc array

  5. Fix an old bug in multixact and two-phase commit. Prepared transactions can