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 <178323411931.108997.17879075456450926050@wrigleys.postgresql.org>
From: "David G. Johnston" <david.g.johnston@gmail.com>
Date: Mon, 6 Jul 2026 08:49:36 -0700
Message-ID: 
 <CAKFQuwZkZb6BXA3ELVQnAZKWk_VL3jcv0ZaQszRq9zRnALJXOA@mail.gmail.com>
Subject: Re: Index Only Scans with functions
To: jb@jbitc.de, pgsql-docs@lists.postgresql.org
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On Mon, Jul 6, 2026 at 8:44=E2=80=AFAM PG Doc comments form <noreply@postgr=
esql.org>
wrote:

> The following documentation comment has been logged on the website:
>
> Page: https://www.postgresql.org/docs/18/indexes-index-only-scans.html
>


> and concludes that an index-only scan is not possible."
>
> I tried to reproduce the behavior, but it used the index (which is good):
>

You haven't demonstrated it using an index ONLY scan which is what that
section is talking about.


>                                                 QUERY PLAN
>
> -------------------------------------------------------------------------=
----------------------------------
>  Index Scan using t_i1 on t  (cost=3D0.42..8.69 rows=3D1 width=3D4) (actu=
al
> time=3D0.034..0.035 rows=3D1.00 loops=3D1)
>
>

David J.

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<div dir=3D"ltr"><div dir=3D"ltr"><div class=3D"gmail_default" style=3D"fon=
t-family:arial,helvetica,sans-serif"><span style=3D"font-family:Arial,Helve=
tica,sans-serif;background-color:transparent">On Mon, Jul 6, 2026 at 8:44=
=E2=80=AFAM PG Doc comments form &lt;<a href=3D"mailto:noreply@postgresql.o=
rg">noreply@postgresql.org</a>&gt; wrote:</span></div></div><div class=3D"g=
mail_quote gmail_quote_container"><blockquote class=3D"gmail_quote" style=
=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding=
-left:1ex">The following documentation comment has been logged on the websi=
te:<br>
<br>
Page: <a href=3D"https://www.postgresql.org/docs/18/indexes-index-only-scan=
s.html" rel=3D"noreferrer" target=3D"_blank">https://www.postgresql.org/doc=
s/18/indexes-index-only-scans.html</a><br></blockquote><div>=C2=A0</div><bl=
ockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-lef=
t:1px solid rgb(204,204,204);padding-left:1ex">and concludes that an index-=
only scan is not possible.&quot;<br>
<br>
I tried to reproduce the behavior, but it used the index (which is good):<b=
r></blockquote><div><br></div><div class=3D"gmail_default" style=3D"font-fa=
mily:arial,helvetica,sans-serif">You haven&#39;t demonstrated it using an i=
ndex ONLY scan which is what that section is talking about.</div><div class=
=3D"gmail_default" style=3D"font-family:arial,helvetica,sans-serif"><br></d=
iv><blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;bord=
er-left:1px solid rgb(204,204,204);padding-left:1ex"><br>
=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 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 QUERY PLAN<br>
---------------------------------------------------------------------------=
--------------------------------<br>
=C2=A0Index Scan using t_i1 on t=C2=A0 (cost=3D0.42..8.69 rows=3D1 width=3D=
4) (actual<br>
time=3D0.034..0.035 rows=3D1.00 loops=3D1)<br>=C2=A0 =C2=A0=C2=A0<br></bloc=
kquote><div><br></div><div class=3D"gmail_default" style=3D"font-family:ari=
al,helvetica,sans-serif">David J.</div><div class=3D"gmail_default" style=
=3D"font-family:arial,helvetica,sans-serif"><br></div></div></div>

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