From: Antonin Houska <ah@cybertec.at>
To: Chao Li <li.evan.chao@gmail.com>
cc: Postgres hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: repack: fix uninitialized DecodingWorkerShared.initialized
In-reply-to: <9AFE5694-9420-40C3-842C-4A4473E1D02B@gmail.com>
References: <9AFE5694-9420-40C3-842C-4A4473E1D02B@gmail.com>
Comments: In-reply-to Chao Li <li.evan.chao@gmail.com>
   message dated "Wed, 15 Apr 2026 18:22:44 +0800."
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Date: Wed, 15 Apr 2026 17:07:32 +0200
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Chao Li <li.evan.chao@gmail.com> wrote:

> I have not reviewed the repack-related patches before. Recently, I starte=
d trying to understand how repack works and trace through the code.

Thanks, I appreciate that!

> While tracing start_repack_decoding_worker(), I noticed something suspici=
ous:
>=20
> ```
> 	seg =3D dsm_create(size, 0);
> 	shared =3D (DecodingWorkerShared *) dsm_segment_address(seg);
> 	shared->lsn_upto =3D InvalidXLogRecPtr;
> 	shared->done =3D false;
> 	SharedFileSetInit(&shared->sfs, seg);
> 	shared->last_exported =3D -1;
> 	SpinLockInit(&shared->mutex);
> 	shared->dbid =3D MyDatabaseId;
> ```
>=20
> Here, the code creates a shared-memory segment and lets =E2=80=9Cshared" =
point to that memory. It then initializes some fields of =E2=80=9Cshared". =
However, later code reads shared->initialized, but this field was not initi=
alized:

The problem was noticed earlier this week and I already posted a fix [1].

> For the fix, since start_repack_decoding_worker() is not on a hot path, I=
 think it is fine to zero the whole shared struct explicitly, and then init=
ialize the non-zero fields afterwards.

Although not strongly, I prefer setting individual fields explicitly.


[1] https://www.postgresql.org/message-id/182883.1776073323%40localhost

--=20
Antonin Houska
Web: https://www.cybertec-postgresql.com