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

Sami Imseih <samimseih@gmail.com>

From: Sami Imseih <samimseih@gmail.com>

To: Yura Sokolov <y.sokolov@postgrespro.ru>

Cc: Heikki Linnakangas <hlinnaka@iki.fi>, "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>, Chao Li <li.evan.chao@gmail.com>

Date: 2026-03-02T02:34:13Z

Lists: pgsql-hackers

> New version attached.

The comment here:

+static inline MultiXactId *
+PreparedXactOldestMemberMXactIdSlot(ProcNumber procno)
+{
+       /*
+        * The entries with indexes >= MaxBackends in the OldestMemberMXactId
+        * array are reserved for regular backends.

should say "array are reserved for prepared transactions"

otherwise, LGTM.

--
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 →

Add test for row-locking and multixids with prepared transactions
- 969576dab47b 17.10 landed
- fa3b328e6dc5 18.4 landed
- fe08113aefc9 19 (unreleased) landed
Skip prepared_xacts test if max_prepared_transactions < 2
- ffe53037dff7 14.23 landed
- a6b11ac4c42d 15.18 landed
- 65f5c451a3e1 16.14 landed
- 80d1d4ee06fd 17.10 landed
- 201436c19f40 18.4 landed
- 19615a44b3e6 19 (unreleased) landed
Fix OldestMemberMXactId and OldestVisibleMXactId array usage
- dcd9c06a4203 17.10 landed
- 0a50ef094382 18.4 landed
- ccae90abdbb6 19 (unreleased) landed
Redefine backend ID to be an index into the proc array
- ab355e3a88de 17.0 cited
Fix an old bug in multixact and two-phase commit. Prepared transactions can
- cd87b6f8a508 9.0.0 cited