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Subject: Re: Fix bug in multixact Oldest*MXactId initialization and access
From: Chao Li <li.evan.chao@gmail.com>
In-Reply-To: <bf2951b4-687b-4bd3-a072-46deb463f177@postgrespro.ru>
Date: Fri, 27 Feb 2026 15:48:17 +0800
Cc: "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>,
 Heikki Linnakangas <hlinnaka@iki.fi>,
 Andres Freund <andres@anarazel.de>,
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To: Yura Sokolov <y.sokolov@postgrespro.ru>
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> On Feb 27, 2026, at 00:22, Yura Sokolov <y.sokolov@postgrespro.ru> =
wrote:
>=20
>=20
> Chao Li, new access functions doen't branch because I've made separate
> functions to store at slots for prepared transactions.
>=20

```
+	OldestMemberMXactId[procno - MaxChildren + MaxBackends] =3D =
mxact;
```

Wow, this is clever. It removes NUM_AUXILIARY_PROCS from procno without =
introducing an extra if check.

However, I am not a big fan of the new global variable names:
```
MaxChildren =3D MaxBackends + NUM_AUXILIARY_PROCS;
TotalProcs =3D MaxChildren + max_prepared_xacts;
TotalXactProcs =3D MaxBackends + max_prepared_xacts;
```

MaxChildren is actually the total number of backends plus auxiliary =
processes. Maybe something like MaxProcs would better reflect that?

TotalProcs is really the length of the PGPROC array in shared memory. =
Prepared transactions are not real processes; they just occupy some =
slots in the proc array. So perhaps a name like MaxPGProcSlots or =
MaxBackendAndPreparedSlots would be more accurate.

As for TotalXactProcs, maybe something like MaxBackendAndPreparedSlots =
would make the intent clearer.

Anyway, I am not very good at naming things. You or others may have =
better suggestions.

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/