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From: Koen De Groote <kdg.dev@gmail.com>
Date: Sat, 12 Oct 2024 20:32:04 +0200
Message-ID: <CAGbX52FkdEqnr=JvRDY0yr0tsk2PGtfaejj3eA18jvYcmfQFnw@mail.gmail.com>
Subject: Re: Foreign Data Wrapper behavior?
To: Adrian Klaver <adrian.klaver@aklaver.com>
Cc: PostgreSQL General <pgsql-general@lists.postgresql.org>
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Ah, thanks for that

On Fri, Oct 11, 2024 at 5:59=E2=80=AFPM Adrian Klaver <adrian.klaver@aklave=
r.com>
wrote:

> On 10/11/24 04:08, Koen De Groote wrote:
> > In the release notes for postgres 17 I'm reading:
> >
> >  > The PostgreSQL foreign data wrapper (postgres_fdw), used to execute
> > queries on remote PostgreSQL instances, can now push EXISTS and IN
> > subqueries to the remote server for more efficient processing.
> >
> > I'm confused as to what this means. In older versions, are parts of
> > queries not sent to the foreign server? Or is this change meant to impl=
y
> > the sending of only the subqueries, the result of which is then directl=
y
> > used in pushing the entire query?
> >
> > Or am I still wrong as to what this means?
> >
> > I looked at the documentation and there doesn't seem to be any
> > indication of particular queries not being pushed to the foreign server=
,
> > so this wording that "can now push EXISTS and IN subqueries to the
> > remote server" is confusing.
> >
> > What am I missing?
>
> Read:
>
>
> https://www.postgresql.org/docs/current/postgres-fdw.html#POSTGRES-FDW-RE=
MOTE-QUERY-OPTIMIZATION
>
> F.36.5. Remote Query Optimization
>
>
> As to the change in the Release Note see the --hackers discussion:
>
>
> https://www.postgresql.org/message-id/c9e2a757cf3ac2333714eaf83a9cc184%40=
postgrespro.ru
>
> >
> > Regards,
> > Koen De Groote
>
> --
> Adrian Klaver
> adrian.klaver@aklaver.com
>
>

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<div dir=3D"ltr">Ah, thanks for that<br></div><br><div class=3D"gmail_quote=
"><div dir=3D"ltr" class=3D"gmail_attr">On Fri, Oct 11, 2024 at 5:59=E2=80=
=AFPM Adrian Klaver &lt;<a href=3D"mailto:adrian.klaver@aklaver.com">adrian=
.klaver@aklaver.com</a>&gt; wrote:<br></div><blockquote class=3D"gmail_quot=
e" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204)=
;padding-left:1ex">On 10/11/24 04:08, Koen De Groote wrote:<br>
&gt; In the release notes for postgres 17 I&#39;m reading:<br>
&gt; <br>
&gt;=C2=A0 &gt; The PostgreSQL foreign data wrapper (postgres_fdw), used to=
 execute <br>
&gt; queries on remote PostgreSQL instances, can now push EXISTS and IN <br=
>
&gt; subqueries to the remote server for more efficient processing.<br>
&gt; <br>
&gt; I&#39;m confused as to what this means. In older versions, are parts o=
f <br>
&gt; queries not sent to the foreign server? Or is this change meant to imp=
ly <br>
&gt; the sending of only the subqueries, the result of which is then direct=
ly <br>
&gt; used in pushing the entire query?<br>
&gt; <br>
&gt; Or am I still wrong as to what this means?<br>
&gt; <br>
&gt; I looked at the documentation and there doesn&#39;t seem to be any <br=
>
&gt; indication of particular queries not being pushed to the foreign serve=
r, <br>
&gt; so this wording that &quot;can now push EXISTS and IN subqueries to th=
e <br>
&gt; remote server&quot; is confusing.<br>
&gt; <br>
&gt; What am I missing?<br>
<br>
Read:<br>
<br>
<a href=3D"https://www.postgresql.org/docs/current/postgres-fdw.html#POSTGR=
ES-FDW-REMOTE-QUERY-OPTIMIZATION" rel=3D"noreferrer" target=3D"_blank">http=
s://www.postgresql.org/docs/current/postgres-fdw.html#POSTGRES-FDW-REMOTE-Q=
UERY-OPTIMIZATION</a><br>
<br>
F.36.5. Remote Query Optimization<br>
<br>
<br>
As to the change in the Release Note see the --hackers discussion:<br>
<br>
<a href=3D"https://www.postgresql.org/message-id/c9e2a757cf3ac2333714eaf83a=
9cc184%40postgrespro.ru" rel=3D"noreferrer" target=3D"_blank">https://www.p=
ostgresql.org/message-id/c9e2a757cf3ac2333714eaf83a9cc184%40postgrespro.ru<=
/a><br>
<br>
&gt; <br>
&gt; Regards,<br>
&gt; Koen De Groote<br>
<br>
-- <br>
Adrian Klaver<br>
<a href=3D"mailto:adrian.klaver@aklaver.com" target=3D"_blank">adrian.klave=
r@aklaver.com</a><br>
<br>
</blockquote></div>

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