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From: Dimitrios Apostolou <[email protected]>
To: Thomas Munro <[email protected]>
Cc: Tomas Vondra <[email protected]>
Cc: [email protected]
Cc: Andres Freund <[email protected]>
Cc: Melanie Plageman <[email protected]>
Cc: Heikki Linnakangas <[email protected]>
Cc: Kyotaro Horiguchi <[email protected]>
Cc: David Rowley <[email protected]>
Subject: Re: [PING] fallocate() causes btrfs to never compress postgresql files
Date: Thu, 12 Jun 2025 14:41:18 +0200 (CEST)
Message-ID: <[email protected]> (raw)
In-Reply-To: <CA+hUKGLib4Wo9n637HCq2BvOrczwvzReGTHWdyYKn6_KXUP2ag@mail.gmail.com>
References: <[email protected]>
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On Mon, 9 Jun 2025, Thomas Munro wrote:

> On Tue, Jun 3, 2025 at 1:58 AM Dimitrios Apostolou <[email protected]> wrote:
>> This sounds like the best solution IMO. People can then experiment with
>> different settings and filesystems, and that way we also learn in the
>> process. Thank you for the effort and patches so far.
>
> OK, here's a basic patch to experiment with.  You can set:
>
> file_extend_method = fallocate,ftruncate,write
> file_extend_method_threshold = 8 # (below 8 always write, 0 means never write)
>

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?

Dimitris

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