From: Antonin Houska <ah@cybertec.at>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
cc: Srinath Reddy Sadipiralla <srinath2133@gmail.com>,
    Tom Lane <tgl@sss.pgh.pa.us>, Andres Freund <andres@anarazel.de>,
    Noah Misch <noah@leadboat.com>, 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]
In-reply-to: <202604070916.5rj6kvjx3mrk@alvherre.pgsql>
References: <202604070916.5rj6kvjx3mrk@alvherre.pgsql>
Comments: In-reply-to Alvaro Herrera <alvherre@alvh.no-ip.org>
   message dated "Tue, 07 Apr 2026 11:22:18 +0200."
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Date: Tue, 07 Apr 2026 11:35:50 +0200
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Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:

> On 2026-Apr-07, Antonin Houska wrote:
> =

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

> Yeah, apparently it keeps track of tainted bytes somehow.  Clever.
> =

> The change to palloc0() that I was proposing did not fix the problem,
> because the stack allocated struct overwrote those zeroes with the
> uninitialized padding bytes.
> =

> I ended up with an equivalent fix to Srinath's -- zero-initializing
> the stack-allocated struct, so that the bytes that end up copied by
> memcpy() are all defined.  Srinath confirmed that in his environment the
> valgrind failure goes away, so I think we're good.

Thanks!

-- =

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