Date: Mon, 05 Jun 2023 17:15:24 +0200
From: Tim Schwenke <tim@trallnag.com>
To: "David G. Johnston" <david.g.johnston@gmail.com>
Cc: "Pgsql Novice" <pgsql-novice@lists.postgresql.org>
Message-Id: <1888c20926e.d2fc55ae8791.8729366224157085719@trallnag.com>
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Subject: Re: Does PostgreSQL cache all columns of a table after SELECT?
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Thanks, you all helped me


---- On Mon, 05 Jun 2023 16:26:08 +0200 David G. Johnston <david.g.johnston=
@gmail.com> wrote ---


On Mon, Jun 5, 2023, 06:17 Tim Schwenke <mailto:tim@trallnag.com> wrote:

Hello David,
=20
 from what I understand, in PostgreSQL, tables are stored in one or more fi=
les called segments. There is no separation by columns.
=20
 https://www.postgresql.org/docs/8.1/storage.html
=20
 This means if I select a single column from a table the first time, the fu=
ll file / segment is read and put into page cache if there is enough space.


Pages are subsegment.


You may also wish to take care to notice the version of documentation pages=
 you look at and reference.=C2=A0 8.1 is long past its expiration date.


David J.
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head>=
<meta content=3D"text/html;charset=3DUTF-8" http-equiv=3D"Content-Type"></h=
ead><body ><div style=3D"font-family: Verdana, Arial, Helvetica, sans-serif=
; font-size: 10pt;"><div>Thanks, you all helped me</div><div><br></div><div=
 class=3D"zmail_extra_hr" style=3D"border-top: 1px solid rgb(204, 204, 204)=
; height: 0px; margin-top: 10px; margin-bottom: 10px; line-height: 0px;"><b=
r></div><div class=3D"zmail_extra" data-zbluepencil-ignore=3D"true"><div><b=
r></div><div id=3D"Zm-_Id_-Sgn1">---- On Mon, 05 Jun 2023 16:26:08 +0200 <b=
>David G. Johnston &lt;david.g.johnston@gmail.com&gt;</b> wrote ---<br></di=
v><div><br></div><blockquote id=3D"blockquote_zmail" style=3D"margin: 0px;"=
><div><div dir=3D"auto"><div><div class=3D"x_1434821918gmail_quote"><div di=
r=3D"ltr" class=3D"x_1434821918gmail_attr">On Mon, Jun 5, 2023, 06:17 Tim S=
chwenke &lt;<a href=3D"mailto:tim@trallnag.com" target=3D"_blank">tim@trall=
nag.com</a>&gt; wrote:<br></div><blockquote class=3D"x_1434821918gmail_quot=
e" style=3D"margin: 0 0 0 0.8ex;border-left: 1.0px rgb(204,204,204) solid;p=
adding-left: 1.0ex;">Hello David,<br> <br> from what I understand, in Postg=
reSQL, tables are stored in one or more files called segments. There is no =
separation by columns.<br> <br> <a href=3D"https://www.postgresql.org/docs/=
8.1/storage.html" target=3D"_blank">https://www.postgresql.org/docs/8.1/sto=
rage.html</a><br> <br> This means if I select a single column from a table =
the first time, the full file / segment is read and put into page cache if =
there is enough space.</blockquote></div></div><div dir=3D"auto"><br></div>=
<div dir=3D"auto">Pages are subsegment.<br></div><div dir=3D"auto"><br></di=
v><div dir=3D"auto">You may also wish to take care to notice the version of=
 documentation pages you look at and reference.&nbsp; 8.1 is long past its =
expiration date.<br></div><div dir=3D"auto"><br></div><div dir=3D"auto">Dav=
id J.<br></div></div></div></blockquote></div></div><br></body></html>
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