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From: Rahila Syed <rahilasyed90@gmail.com>
Date: Fri, 19 Sep 2025 18:42:32 +0530
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Subject: Re: Use WALReadFromBuffers in more places
To: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
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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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<div dir=3D"ltr"><div dir=3D"ltr">Hi Bharath,<div><br></div></div><div clas=
s=3D"gmail_quote gmail_quote_container"><div dir=3D"ltr" class=3D"gmail_att=
r"><br></div><blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px =
0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Hi,<br>
<br>
Commit 91f2cae7a4e that introduced WALReadFromBuffers only used it for<br>
physical walsenders. It can also be used in more places benefitting<br>
logical walsenders, backends running pg_walinspect and logical<br>
decoding functions if the WAL is available in WAL buffers. I&#39;m<br>
attaching a 0001 patch for this.<br><br></blockquote><div>=C2=A0</div><div>=
Thank=C2=A0you for=C2=A0working on this. It seems like a useful optimizatio=
n. Do you have any information <br>on how much this improves the performanc=
e of the new callers of WALReadFromBuffers?</div><div><br></div><div>Regard=
ing the v3 version of the patch, do you also intend to include other caller=
s of WALRead,</div><div>such as walsummarizer.c and pg_waldump.c?=C2=A0=C2=
=A0</div><div><br>In WALReadFromBuffers, the buffer scan currently stops wh=
en it encounters a buffer that</div><div>doesn&#39;t have the needed WAL pa=
ge. However, it&#39;s possible to continue scanning past the <br>missing pa=
ge and find other relevant pages further along. By keeping track of which p=
ages <br>are missing, we could read only those specific pages from files, i=
nstead of reading everything <br>after the first missing page. I am wonderi=
ng if this was taken into account during the design <br>of the function.=C2=
=A0<br><br>Thank you,</div><div>Rahila Syed</div></div></div>

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