Horton

Re: [PING] fallocate() causes btrfs to never compress postgresql files

Magnus Hagander <magnus@hagander.net>

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From: Magnus Hagander <magnus@hagander.net>
To: Thomas Munro <thomas.munro@gmail.com>
Cc: Dimitrios Apostolou <jimis@gmx.net>, Tomas Vondra <tomas@vondra.me>, pgsql-hackers@lists.postgresql.org, Andres Freund <andres@anarazel.de>, Melanie Plageman <melanieplageman@gmail.com>, Heikki Linnakangas <hlinnaka@iki.fi>, Kyotaro Horiguchi <horikyota.ntt@gmail.com>, David Rowley <dgrowleyml@gmail.com>
Date: 2025-07-29T06:52:34Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Add file_extend_method=posix_fallocate,write_zeros.

  2. Add smgrzeroextend(), FileZero(), FileFallocate()

On Fri, Jul 11, 2025 at 12:45 AM Thomas Munro <thomas.munro@gmail.com>
wrote:

> On Fri, Jul 11, 2025 at 5:39 AM Dimitrios Apostolou <jimis@gmx.net> wrote:
> > > I applied the patch on PostgreSQL v17 and am testing it now. I chose
> > > ftruncate method and I see ftruncate in action using strace while doing
> > > pg_restore of a big database. Nothing unexpected has happened so far.
> I also
> > > verified that files are being compressed, obeying Btrfs's mount option
> > > compress=zstd.
> > >
> > > Thanks for the patch! What are the odds of commiting it to v17?
> >
> > Ping. :-)
> > Patch behaves good for me. Any chance of applying it and backporting it?
>
> Yeah, this seems to make sense, as it is a pretty bad regression for
> people who are counting on BTRFS compression for their large database.
> Not so sure about the threshold bit -- I'd probably leave that out of
> the backport in the interest of stable branch-minimalism.  Anyone have
> any better ideas, better naming, or objections?
>

Not just to throw a wrench in there, but... Should this perhaps be a
tablespace option? ISTM having different filesystems for them is a good
reason to use tablespaces in the first place, and then being able to pick
different options...

-- 
 Magnus Hagander
 Me: https://www.hagander.net/ <http://www.hagander.net/>
 Work: https://www.redpill-linpro.com/ <http://www.redpill-linpro.com/>