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From: Rahila Syed <[email protected]>
To: Bharath Rupireddy <[email protected]>
Cc: PostgreSQL-development <[email protected]>
Subject: Re: Use WALReadFromBuffers in more places
Date: Fri, 19 Sep 2025 18:42:32 +0530
Message-ID: <CAH2L28vxZg0PgiweVw=FqczD0zJC+Ud9+=H2yP-GPJeE2NwDQw@mail.gmail.com> (raw)
In-Reply-To: <CALj2ACVfF2Uj9NoFy-5m98HNtjHpuD17EDE9twVeJng-jTAe7A@mail.gmail.com>
References: <CALj2ACVfF2Uj9NoFy-5m98HNtjHpuD17EDE9twVeJng-jTAe7A@mail.gmail.com>

Hi Bharath,


Hi,
>
> Commit 91f2cae7a4e that introduced WALReadFromBuffers only used it for
> physical walsenders. It can also be used in more places benefitting
> logical walsenders, backends running pg_walinspect and logical
> decoding functions if the WAL is available in WAL buffers. I'm
> attaching a 0001 patch for this.
>
>
Thank you for working on this. It seems like a useful optimization. Do you
have any information
on how much this improves the performance of the new callers of
WALReadFromBuffers?

Regarding the v3 version of the patch, do you also intend to include other
callers of WALRead,
such as walsummarizer.c and pg_waldump.c?

In WALReadFromBuffers, the buffer scan currently stops when it encounters a
buffer that
doesn't have the needed WAL page. However, it's possible to continue
scanning past the
missing page and find other relevant pages further along. By keeping track
of which pages
are missing, we could read only those specific pages from files, instead of
reading everything
after the first missing page. I am wondering if this was taken into account
during the design
of the function.

Thank you,
Rahila Syed

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