MIME-Version: 1.0
References: <20181105161231.GA13780@momjian.us>
 <20181105170112.dtxazkxcyuoszfi2@alvherre.pgsql>
 <20181106184220.GA31546@momjian.us>
In-Reply-To: <20181106184220.GA31546@momjian.us>
From: Nikolay Samokhvalov <samokhvalov@gmail.com>
Date: Mon, 4 Nov 2019 02:35:51 +0300
Message-ID: 
 <CANNMO+Jzi2Pm6OF=g9LxZmSK9mmoRSYc1nrZeQjoEq=SyCCGog@mail.gmail.com>
Subject: Re: effective_cache_size
To: Bruce Momjian <bruce@momjian.us>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>, nat@makarevitch.org,
	peter.eisentraut@2ndquadrant.com, pgsql-docs@lists.postgresql.org
Content-Type: multipart/alternative; boundary="000000000000877170059679a9fc"
Precedence: bulk

--000000000000877170059679a9fc
Content-Type: text/plain; charset="UTF-8"

A follow-up on this:

Should documentation also mention that it does not make sense to set
effective_cache_size < shared_buffers? And maybe it is worth prohibiting
this or at least having a WARNING in logs?

Why: I see setups where with growing RAM and shared_buffers set to 25%,
effective_cache_size remains untuned, at some point significantly below the
value of shared_buffers.

On Tue, Nov 6, 2018 at 21:42 Bruce Momjian <bruce@momjian.us> wrote:

> On Mon, Nov  5, 2018 at 02:01:12PM -0300, Alvaro Herrera wrote:
> > On 2018-Nov-05, Bruce Momjian wrote:
> >
> > > Well, here are the lines in guc.c:
> > >
> > >             gettext_noop("Sets the planner's assumption about the size
> of the data cache."),
> > >             gettext_noop("That is, the size of the cache used for
> PostgreSQL data files. "
> > >                          "This is measured in disk pages, which are
> normally 8 kB each."),
> >
> > I suggest "the size of data caches", plural, in the first line (two
> > letters shorter, since I lost the article).  And in the second line, use
> > "... the size of the combined caches used for Pg data files, including
> > both the kernel cache and shared buffers" -- a few words longer, which
> > seems worth it to me.
>
> OK, I handled it slightly differently:
>
>
> https://git.postgresql.org/pg/commitdiff/b43df566b372650a9b9e2a0dd9e695c1f16da14f
>
> I think "the size of" anything plural is confusing so I said "the total
> size of".
>
> --
>   Bruce Momjian  <bruce@momjian.us>        http://momjian.us
>   EnterpriseDB                             http://enterprisedb.com
>
> + As you are, so once was I.  As I am, so you will be. +
> +                      Ancient Roman grave inscription +
>

--000000000000877170059679a9fc
Content-Type: text/html; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

<div><div dir=3D"auto">A follow-up on this:</div></div><div dir=3D"auto"><b=
r></div><div dir=3D"auto">Should documentation also mention that it does no=
t make sense to set effective_cache_size &lt; shared_buffers? And maybe it =
is worth prohibiting this or at least having a WARNING in logs?</div><div d=
ir=3D"auto"><br></div><div dir=3D"auto">Why: I see setups where with growin=
g RAM and shared_buffers set to 25%, effective_cache_size remains untuned, =
at some point significantly below the value of shared_buffers.</div><div><b=
r><div class=3D"gmail_quote"><div dir=3D"ltr" class=3D"gmail_attr">On Tue, =
Nov 6, 2018 at 21:42 Bruce Momjian &lt;<a href=3D"mailto:bruce@momjian.us">=
bruce@momjian.us</a>&gt; wrote:<br></div><blockquote class=3D"gmail_quote" =
style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">On =
Mon, Nov=C2=A0 5, 2018 at 02:01:12PM -0300, Alvaro Herrera wrote:<br>
&gt; On 2018-Nov-05, Bruce Momjian wrote:<br>
&gt; <br>
&gt; &gt; Well, here are the lines in guc.c:<br>
&gt; &gt; <br>
&gt; &gt;=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0gettext_noop(&quot=
;Sets the planner&#39;s assumption about the size of the data cache.&quot;)=
,<br>
&gt; &gt;=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0gettext_noop(&quot=
;That is, the size of the cache used for PostgreSQL data files. &quot;<br>
&gt; &gt;=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 =C2=A0 =C2=A0 =C2=A0 &quot;This is measured in disk pages, which are no=
rmally 8 kB each.&quot;),<br>
&gt; <br>
&gt; I suggest &quot;the size of data caches&quot;, plural, in the first li=
ne (two<br>
&gt; letters shorter, since I lost the article).=C2=A0 And in the second li=
ne, use<br>
&gt; &quot;... the size of the combined caches used for Pg data files, incl=
uding<br>
&gt; both the kernel cache and shared buffers&quot; -- a few words longer, =
which<br>
&gt; seems worth it to me.<br>
<br>
OK, I handled it slightly differently:<br>
<br>
=C2=A0 =C2=A0 =C2=A0 =C2=A0 <a href=3D"https://git.postgresql.org/pg/commit=
diff/b43df566b372650a9b9e2a0dd9e695c1f16da14f" rel=3D"noreferrer" target=3D=
"_blank">https://git.postgresql.org/pg/commitdiff/b43df566b372650a9b9e2a0dd=
9e695c1f16da14f</a><br>
<br>
I think &quot;the size of&quot; anything plural is confusing so I said &quo=
t;the total<br>
size of&quot;.<br>
<br>
-- <br>
=C2=A0 Bruce Momjian=C2=A0 &lt;<a href=3D"mailto:bruce@momjian.us" target=
=3D"_blank">bruce@momjian.us</a>&gt;=C2=A0 =C2=A0 =C2=A0 =C2=A0 <a href=3D"=
http://momjian.us" rel=3D"noreferrer" target=3D"_blank">http://momjian.us</=
a><br>
=C2=A0 EnterpriseDB=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0<a href=3D"http://enterpris=
edb.com" rel=3D"noreferrer" target=3D"_blank">http://enterprisedb.com</a><b=
r>
<br>
+ As you are, so once was I.=C2=A0 As I am, so you will be. +<br>
+=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 Ancient Roman grave inscription +<br>
</blockquote></div></div>

--000000000000877170059679a9fc--