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From: Ron Johnson <ronljohnsonjr@gmail.com>
Date: Mon, 17 Feb 2025 16:40:56 -0500
Message-ID: <CANzqJaDPR_sshr1hXuMsiZQDf7nH4BthNioCHJ4cVcGKxiSg_Q@mail.gmail.com>
Subject: Re: Loading the latest N rows into the cache seems way too fast.
To: pgsql-general <pgsql-general@postgresql.org>
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On Mon, Feb 17, 2025 at 4:36=E2=80=AFPM Tom Lane <tgl@sss.pgh.pa.us> wrote:

> Ron Johnson <ronljohnsonjr@gmail.com> writes:
> > The bigint "id" column in "mytbl" is populated from a sequence, and so =
is
> > monotonically increasing: the newest records will have the biggest id
> > values.
> > The table also has a bytea column that averages about 100KB.
>
> > Loading 200K rows is more than 200MB.  I expected this "prewarm"
> statement
> > to take much longer than 1/2 second.  Am I still in the dark ages of
> > computer speed, or is this statement not doing what I hope it's doing?
>
> It's not pulling in the TOAST storage where the bytea column lives.
> (pg_prewarm wouldn't have either, without special pushups.)
>

Puzzling, since I ran "PERFORM *".  What if I explicitly mentioned the
bytea column's name?

--=20
Death to <Redacted>, and butter sauce.
Don't boil me, I'm still alive.
<Redacted> lobster!

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<div dir=3D"ltr"><div dir=3D"ltr">On Mon, Feb 17, 2025 at 4:36=E2=80=AFPM T=
om Lane &lt;<a href=3D"mailto:tgl@sss.pgh.pa.us">tgl@sss.pgh.pa.us</a>&gt; =
wrote:</div><div class=3D"gmail_quote gmail_quote_container"><blockquote cl=
ass=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid=
 rgb(204,204,204);padding-left:1ex">Ron Johnson &lt;<a href=3D"mailto:ronlj=
ohnsonjr@gmail.com" target=3D"_blank">ronljohnsonjr@gmail.com</a>&gt; write=
s:<br>
&gt; The bigint &quot;id&quot; column in &quot;mytbl&quot; is populated fro=
m a sequence, and so is<br>
&gt; monotonically increasing: the newest records will have the biggest id<=
br>
&gt; values.<br>
&gt; The table also has a bytea column that averages about 100KB.<br>
<br>
&gt; Loading 200K rows is more than 200MB.=C2=A0 I expected this &quot;prew=
arm&quot; statement<br>
&gt; to take much longer than 1/2 second.=C2=A0 Am I still in the dark ages=
 of<br>
&gt; computer speed, or is this statement not doing what I hope it&#39;s do=
ing?<br>
<br>
It&#39;s not pulling in the TOAST storage where the bytea column lives.<br>
(pg_prewarm wouldn&#39;t have either, without special pushups.)<br></blockq=
uote><div><br></div><div>Puzzling, since I ran &quot;PERFORM *&quot;.=C2=A0=
 What if I explicitly=C2=A0mentioned the bytea column&#39;s=C2=A0name?</div=
></div><div><br></div><span class=3D"gmail_signature_prefix">-- </span><br>=
<div dir=3D"ltr" class=3D"gmail_signature"><div dir=3D"ltr">Death to &lt;Re=
dacted&gt;, and butter sauce.<div>Don&#39;t boil me, I&#39;m still alive.<b=
r><div><div>&lt;Redacted&gt; lobster!</div></div></div></div></div></div>

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