Horton

Re: pread() and pwrite()

Thomas Munro <thomas.munro@enterprisedb.com>

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From: Thomas Munro <thomas.munro@enterprisedb.com>
To: Andrew Dunstan <andrew.dunstan@2ndquadrant.com>
Cc: Jesper Pedersen <jesper.pedersen@redhat.com>, Tom Lane <tgl@sss.pgh.pa.us>, Alvaro Herrera <alvherre@2ndquadrant.com>, Magnus Hagander <magnus@hagander.net>, Oskari Saarenmaa <os@ohmu.fi>, Pg Hackers <pgsql-hackers@postgresql.org>, Tobias Oberstein <tobias.oberstein@gmail.com>
Date: 2018-11-07T22:48:52Z
Lists: pgsql-hackers 
On Thu, Nov 8, 2018 at 4:27 AM Andrew Dunstan
<andrew.dunstan@2ndquadrant.com> wrote:
> On 11/7/18 10:05 AM, Jesper Pedersen wrote:
> > On 11/7/18 9:30 AM, Tom Lane wrote:
> >> I'm confused by this.  Surely the pwrite-based code is writing
> >> exactly the
> >> same data as before.  Do we have to conclude that valgrind is
> >> complaining
> >> about passing uninitialized data to pwrite() when it did not complain
> >> about exactly the same thing for write()?
> >>
> >> [ looks ... ]  No, what we have to conclude is that the write-related
> >> suppressions in src/tools/valgrind.supp need to be replaced or augmented
> >> with pwrite-related ones.
> >
> > The attached patch fixes this for me.
> >
> > Unfortunately pwrite* doesn't work for the pwrite64(buf) line.
>
> Works for me. If there's no objection I will commit this.

Thanks for adjusting that.  I suppose I would have known about this if
cfbot checked every patch with valgrind, which I might look into.

I'm a little confused about how an uninitialised value originating in
an OID list finishes up in an xlog buffer, considering that OIDs don't
have padding.

-- 
Thomas Munro
http://www.enterprisedb.com

Commits

  1. Use pg_pread() and pg_pwrite() for data files and WAL.

  2. Provide pg_pread() and pg_pwrite() for random I/O.

  3. Convert some long lists in configure.in to one-line-per-entry style.