From: Antonin Houska <ah@cybertec.at>
To: Srinath Reddy Sadipiralla <srinath2133@gmail.com>
cc: Tom Lane <tgl@sss.pgh.pa.us>, Andres Freund <andres@anarazel.de>,
    Noah Misch <noah@leadboat.com>,
    Alvaro Herrera <alvherre@alvh.no-ip.org>,
    vignesh C <vignesh21@gmail.com>,
    Amit Kapila <amit.kapila16@gmail.com>,
    Mihail Nikalayeu <mihailnikalayeu@gmail.com>,
    Matthias van de Meent <boekewurm+postgres@gmail.com>,
    Pg Hackers <pgsql-hackers@lists.postgresql.org>,
    Robert Treat <rob@xzilla.net>
Subject: Re: Adding REPACK [concurrently]
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Comments: In-reply-to Srinath Reddy Sadipiralla <srinath2133@gmail.com>
   message dated "Tue, 07 Apr 2026 14:12:22 +0530."
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Date: Tue, 07 Apr 2026 10:57:46 +0200
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Srinath Reddy Sadipiralla <srinath2133@gmail.com> wrote:

> Hi Tom,
>=20
> On Tue, Apr 7, 2026 at 10:14=E2=80=AFAM Tom Lane <tgl@sss.pgh.pa.us> wrot=
e:
>=20
>  Maybe you saw this already, but BF member skink is failing on
>  src/test/modules/injection_points/specs/repack.spec:
>=20
>  https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=3Dskink&dt=3D202=
6-04-06%2022%3A50%3A41
>=20
> i looked into this , it seems like valgrind catches the uninitialised pad=
ding bytes, which
> repack worker is writing using BufFileWrite, it seems this fix solved the=
 problem.
>=20
> diff --git a/src/backend/utils/time/snapmgr.c b/src/backend/utils/time/sn=
apmgr.c
> index 2e6197f5f35..f5682b87626 100644
> --- a/src/backend/utils/time/snapmgr.c
> +++ b/src/backend/utils/time/snapmgr.c
> @@ -1739,6 +1739,8 @@ SerializeSnapshot(Snapshot snapshot, char *start_ad=
dress)
>=20=20
>   Assert(snapshot->subxcnt >=3D 0);
>=20=20
> + MemSet(&serialized_snapshot, 0, sizeof(SerializedSnapshotData));
> +
>   /* Copy all required fields */
>   serialized_snapshot.xmin =3D snapshot->xmin;
>   serialized_snapshot.xmax =3D snapshot->xmax;
>=20
> thoughts?

Could you reproduce the failure in your environment?

I haven't thought of this explanation because BufFileWrite() only copies the
data to a buffer in the BufFile structure and BufFileDumpBuffer() writes the
buffer. Maybe valgrind is able to track the copying?

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