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

Heikki Linnakangas <hlinnaka@iki.fi>

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From: Heikki Linnakangas <hlinnaka@iki.fi>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Yura Sokolov <y.sokolov@postgrespro.ru>, Sami Imseih <samimseih@gmail.com>, Chao Li <li.evan.chao@gmail.com>, "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>
Date: 2026-03-03T16:59:34Z
Lists: pgsql-hackers

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On 03/03/2026 17:22, Tom Lane wrote:
> Heikki Linnakangas <hlinnaka@iki.fi> writes:
>> Ok, here's another version of Sami's repro. I realized that it doesn't
>> even need concurrent sessions, so I moved it to the main regression test
>> suite, into the 'prepared_xacts' test. Looks good?
> 
> Not directly relevant to the thing being tested here, but ...
> I wonder if we couldn't reduce future maintenance effort for
> prepared_xacts_1.out by modifying that test script to make an
> early exit if prepared transactions are disabled.

+1, I was just thinking the same.

Here's a patch to do that. I'll backpatch this to all supported 
versions, to make backpatching test changes less painful in the future.

- Heikki

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