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From: Riku Iki <[email protected]>
To: Thomas Munro <[email protected]>
Cc: [email protected]
Subject: Re: Preallocation changes in Postgresql 16
Date: Fri, 26 Apr 2024 16:15:35 -0700
Message-ID: <CAMazQQewmq3Zt+mF1JOTTpJyNyhKQT7C_G7z+MjGxs-xRq0Mxw@mail.gmail.com> (raw)
In-Reply-To: <CA+hUKGLu-oDokjt=Hyb8cLPTm19s5HZSq0PY-jXBP6-u2cqMEg@mail.gmail.com>
References: <CAMazQQfp+3f8tD_Q23rCR=O+Jj4jouSRVigbD8OmrTOfHV+8gA@mail.gmail.com>
	<CA+hUKGLu-oDokjt=Hyb8cLPTm19s5HZSq0PY-jXBP6-u2cqMEg@mail.gmail.com>

Thank you, I have such a system. I think my task would be to compile PG
from sources(need to learn this), and see how it works with and without
that code block.

On Thu, Apr 25, 2024 at 2:25 PM Thomas Munro <[email protected]> wrote:

> On Fri, Apr 26, 2024 at 4:37 AM Riku Iki <[email protected]> wrote:
> > I am wondering if there were preallocation related changes in PG16, and
> if it is possible to disable preallocation in PostgreSQL 16?
>
> I have no opinion on the btrfs details, but I was wondering if someone
> might show up with a system that doesn't like that change.  Here is a
> magic 8, tuned on "some filesystems":
>
>         /*
>          * If available and useful, use posix_fallocate() (via
>          * FileFallocate()) to extend the relation. That's often more
>          * efficient than using write(), as it commonly won't cause the
> kernel
>          * to allocate page cache space for the extended pages.
>          *
>          * However, we don't use FileFallocate() for small extensions, as
> it
>          * defeats delayed allocation on some filesystems. Not clear where
>          * that decision should be made though? For now just use a cutoff
> of
>          * 8, anything between 4 and 8 worked OK in some local testing.
>          */
>         if (numblocks > 8)
>
> I wonder if it wants to be a GUC.
>

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