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From: Lakshmi N <lakshmin.jhs@gmail.com>
Date: Thu, 26 Mar 2026 01:06:37 -0700
Message-ID: 
 <CA+3i_M-nu4GcVf6NHf_M5p_-rY2ag7hO8aMfiPRhAB57UwBLZg@mail.gmail.com>
Subject: Re: log XLogPrefetch stats at end of recovery
To: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Cc: Jakub Wartak <jakub.wartak@enterprisedb.com>,
 Thomas Munro <thomas.munro@gmail.com>,
	SATYANARAYANA NARLAPURAM <satyanarlapuram@gmail.com>,
 pgsql-hackers@postgresql.org
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Hi,

On Tue, Mar 24, 2026 at 8:23=E2=80=AFPM Bharath Rupireddy <
bharath.rupireddyforpostgres@gmail.com> wrote:

> Hi,
>
> On Tue, Mar 24, 2026 at 5:07=E2=80=AFAM Lakshmi N <lakshmin.jhs@gmail.com=
> wrote:
> >
> >> so instead of like:
> >> redo prefetch stats: prefetch=3D%lu, hit=3D%lu, skip_init=3D%lu,
> >> skip_new=3D%lu, skip_fpw=3D%lu, skip_rep=3D%lu"
> >>
> >> something like below ones:
> >> redo prefetch stats: done %lu prefetches, %lu hit, %lu zero-initated, =
..
> >> redo prefetch stats: done %lu prefetches, (%d% hit ratio), %lu
> >> zero-initated, .. or something like that
> >
> > Please find the attached patch with the suggested changes. I referenced
> [1] to log the message as suggested.
> >
> > 2026-03-24 04:53:15.251 PDT [18898] LOG:  redo prefetch stats:
> prefetched 27 blocks, skipped 22 blocks because they were already in the
> buffer pool, skipped 17 blocks because they would be zero-initialized,
> skipped 0 blocks because they didn't exist yet, skipped 28 blocks because=
 a
> full page image was included in the WAL, skipped 155 blocks because they
> were already recently prefetched.
>
> IMHO, the above looks too verbose. +1 for Jakub's suggestion. Would
> something like the below work? I believe the developers looking at
> these logs for analysis will have some understanding of what each of
> these means.
>
> LOG: redo prefetch stats: prefetched 27, skipped (22 in buffer pool,
> 17 zero-inited, 0 non-existent, 28 FPI, 155 recently prefetched)
>

Address this in the attached patch. Please let me know if this looks good.
2026-03-26 00:51:19.797 PDT [91881] LOG:  redo prefetch stats: prefetched
418376 blocks, skipped (362419 in the buffer pool, 418479 zero-initialized,
0 non-existent, 9 full page image, 39183318 recently prefetched)

Regards,
Lakshmi

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<div dir=3D"ltr"><div>Hi,</div><br><div class=3D"gmail_quote gmail_quote_co=
ntainer"><div dir=3D"ltr" class=3D"gmail_attr">On Tue, Mar 24, 2026 at 8:23=
=E2=80=AFPM Bharath Rupireddy &lt;<a href=3D"mailto:bharath.rupireddyforpos=
tgres@gmail.com">bharath.rupireddyforpostgres@gmail.com</a>&gt; wrote:<br><=
/div><blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;bo=
rder-left:1px solid rgb(204,204,204);padding-left:1ex">Hi,<br>
<br>
On Tue, Mar 24, 2026 at 5:07=E2=80=AFAM Lakshmi N &lt;<a href=3D"mailto:lak=
shmin.jhs@gmail.com" target=3D"_blank">lakshmin.jhs@gmail.com</a>&gt; wrote=
:<br>
&gt;<br>
&gt;&gt; so instead of like:<br>
&gt;&gt; redo prefetch stats: prefetch=3D%lu, hit=3D%lu, skip_init=3D%lu,<b=
r>
&gt;&gt; skip_new=3D%lu, skip_fpw=3D%lu, skip_rep=3D%lu&quot;<br>
&gt;&gt;<br>
&gt;&gt; something like below ones:<br>
&gt;&gt; redo prefetch stats: done %lu prefetches, %lu hit, %lu zero-initat=
ed, ..<br>
&gt;&gt; redo prefetch stats: done %lu prefetches, (%d% hit ratio), %lu<br>
&gt;&gt; zero-initated, .. or something like that<br>
&gt;<br>
&gt; Please find the attached patch with the suggested changes. I reference=
d [1] to log the message as suggested.<br>
&gt;<br>
&gt; 2026-03-24 04:53:15.251 PDT [18898] LOG:=C2=A0 redo prefetch stats: pr=
efetched 27 blocks, skipped 22 blocks because they were already in the buff=
er pool, skipped 17 blocks because they would be zero-initialized, skipped =
0 blocks because they didn&#39;t exist yet, skipped 28 blocks because a ful=
l page image was included in the WAL, skipped 155 blocks because they were =
already recently prefetched.<br>
<br>
IMHO, the above looks too verbose. +1 for Jakub&#39;s suggestion. Would<br>
something like the below work? I believe the developers looking at<br>
these logs for analysis will have some understanding of what each of<br>
these means.<br>
<br>
LOG: redo prefetch stats: prefetched 27, skipped (22 in buffer pool,<br>
17 zero-inited, 0 non-existent, 28 FPI, 155 recently prefetched)<br></block=
quote><div><br></div><div>Address this in the attached patch. Please let me=
 know if this looks good.</div><div>2026-03-26 00:51:19.797 PDT [91881] LOG=
: =C2=A0redo prefetch stats: prefetched 418376 blocks, skipped (362419 in t=
he buffer pool, 418479 zero-initialized, 0 non-existent, 9 full page image,=
 39183318 recently prefetched)</div><div>=C2=A0</div><div>Regards,</div><di=
v>Lakshmi</div></div></div>

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