Horton

Re: Fix parallel vacuum buffer usage reporting

Nazir Bilal Yavuz <byavuz81@gmail.com>

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From: Nazir Bilal Yavuz <byavuz81@gmail.com>
To: Masahiko Sawada <sawada.mshk@gmail.com>
Cc: Anthonin Bonnefoy <anthonin.bonnefoy@datadoghq.com>, Alena Rybakina <lena.ribackina@yandex.ru>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2024-05-10T10:25:58Z
Lists: pgsql-hackers

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  1. Fix parallel vacuum buffer usage reporting.

  2. Use bump context for TID bitmaps stored by vacuum

Hi,

Thank you for working on this!

On Wed, 1 May 2024 at 06:37, Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>
> Thank you for further testing! I've pushed the patch.

I realized a behaviour change while looking at 'Use pgBufferUsage for
block reporting in analyze' thread [1]. Since that change applies here
as well, I thought it is better to mention it here.

Before this commit, VacuumPageMiss did not count the blocks if its
read was already completed by other backends [2]. Now,
'pgBufferUsage.local_blks_read + pgBufferUsage.shared_blks_read'
counts every block attempted to be read; possibly double counting if
someone else has already completed the read. I do not know which
behaviour is correct but I wanted to mention this.

[1] https://postgr.es/m/CAO6_Xqr__kTTCLkftqS0qSCm-J7_xbRG3Ge2rWhucxQJMJhcRA%40mail.gmail.com

[2] In the WaitReadBuffers() function, see comment:
        /*
         * Skip this block if someone else has already completed it.  If an
         * I/O is already in progress in another backend, this will wait for
         * the outcome: either done, or something went wrong and we will
         * retry.
         */

-- 
Regards,
Nazir Bilal Yavuz
Microsoft