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help / color / mirror / Atom feedFrom: Antonin Houska <[email protected]>
To: Srinath Reddy Sadipiralla <[email protected]>
Cc: Tom Lane <[email protected]>
Cc: Andres Freund <[email protected]>
Cc: Noah Misch <[email protected]>
Cc: Alvaro Herrera <[email protected]>
Cc: vignesh C <[email protected]>
Cc: Amit Kapila <[email protected]>
Cc: Mihail Nikalayeu <[email protected]>
Cc: Matthias van de Meent <[email protected]>
Cc: Pg Hackers <[email protected]>
Cc: Robert Treat <[email protected]>
Subject: Re: Adding REPACK [concurrently]
Date: Tue, 07 Apr 2026 11:29:17 +0200
Message-ID: <192673.1775554157@localhost> (raw)
In-Reply-To: <188275.1775552266@localhost>
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<188275.1775552266@localhost>
Antonin Houska <[email protected]> wrote:
> Srinath Reddy Sadipiralla <[email protected]> wrote:
>
> > i looked into this , it seems like valgrind catches the uninitialised padding bytes, which
> > repack worker is writing using BufFileWrite, it seems this fix solved the problem.
> >
> > diff --git a/src/backend/utils/time/snapmgr.c b/src/backend/utils/time/snapmgr.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_address)
> >
> > Assert(snapshot->subxcnt >= 0);
> >
> > + MemSet(&serialized_snapshot, 0, sizeof(SerializedSnapshotData));
> > +
> > /* Copy all required fields */
> > serialized_snapshot.xmin = snapshot->xmin;
> > serialized_snapshot.xmax = snapshot->xmax;
> >
> > 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?
Given this message, you may be right:
==1617044== Address 0x12d745e2 is 106 bytes inside a block of size 8,272 client-defined
In my environment, the 'buffer' field starts at offset 80 into the BufFile
structure. We first write 8 bytes into it
BufFileWrite(file, &snap_size, sizeof(snap_size));
followed by the snapshot. Since sizeof(SerializedSnapshotData) is 24, the
offset 106 should be the padding following the 'takenDuringRecovery' field.
--
Antonin Houska
Web: https://www.cybertec-postgresql.com
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Subject: Re: Adding REPACK [concurrently]
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