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From: "Colin 't Hart" <colinthart@gmail.com>
Date: Wed, 21 Jan 2026 17:12:44 +0100
Message-ID: <CAMon-aT92+JQVTD54iwEmPpkFRDHDnhOzZGHMG6GoH_8Qh_EDg@mail.gmail.com>
Subject: Re: pgBadger and postgres_fdw
To: Adrian Klaver <adrian.klaver@aklaver.com>
Cc: PostgreSQL General <pgsql-general@lists.postgresql.org>
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1. Migration from one server to another. Newer OS (Debian 12 vs Ubuntu
20.04), same version of Postgres (17).
2. postgres_fdw is to different databases within the same cluster.
3. 17
4. No new analyze was done; migration was achieved by moving the disks
between the virtual servers. We reindexed all text indexes to allow for the
new glibc version on Debian 12.
5. That's the thing: I have no idea which queries the `fetch 100 from c2`
are associated with because the `c2` seems to be reused for each query. The
psycopg python library generates unique server-side cursor names, but
postgres_fdw doesn't.
6. The 19 slowest queries in a 4 hour period are between 2 and 37 minutes,
with an average of over 10 minutes; they are all `fetch 100 from c2`.

The slowness itself isn't my question here; it was caused by having too few
cores in the new environment, while the application was still assuming the
higher core count and generating too many concurrent processes.

My question is how to identify which connections / queries from
postgres_fdw are generating the `fetch 100 from c2` queries, which, in
turn, may quite possibly lead to a feature request for having these named
uniquely.

Thanks,

Colin

On Wed, 21 Jan 2026 at 16:43, Adrian Klaver <adrian.klaver@aklaver.com>
wrote:

> On 1/21/26 00:18, Colin 't Hart wrote:
> > Hi,
> >
> > One of my clients makes extensive use of postgres_fdw. After a migration
> > performance isn't great. pgBadger reports show the slowest queries all
> > being `fetch 100 from c2`.
> >
> > Anyone have any tricks for being able to associate those fetches with
> > the queries that were used when declaring the server-side cursor?
>
> This is going to need a lot more information. To start:
>
> 1) Migration of what and from what version to what version?
>
> 2) Where are the Postgres databases relative to each other on the network?
>
> 3) What versions of Postgres if not covered in 1.
>
> 4) If Postgres was what was being updated was an analyze done on the
> instances?
>
> 5) Show a complete query using EXPLAIN ANALYZE.
>
> 6) Define slow.
>
> >
> > Thanks,
> >
> > Colin
>
>
> --
> Adrian Klaver
> adrian.klaver@aklaver.com
>

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<div dir=3D"ltr"><div>1. Migration from one server to another. Newer OS (De=
bian 12 vs Ubuntu 20.04), same version of Postgres (17).</div><div>2. postg=
res_fdw is to different databases within the same cluster.</div><div>3. 17<=
/div><div>4. No new analyze was done; migration was achieved by moving the =
disks between the virtual servers. We reindexed all text indexes to allow f=
or the new glibc version on Debian 12.</div><div>5. That&#39;s the thing: I=
 have no idea which queries the `fetch 100 from c2` are associated with bec=
ause the `c2` seems to be reused for each query. The psycopg python library=
 generates unique server-side cursor names, but postgres_fdw doesn&#39;t.</=
div><div>6. The 19 slowest queries in a 4 hour period are between 2 and 37 =
minutes, with an average of over 10 minutes; they are all `fetch 100 from c=
2`.</div><div><br></div><div>The slowness itself isn&#39;t my question here=
; it was caused by having too few cores in the new environment, while the a=
pplication was still assuming the higher core count and generating too many=
 concurrent processes.</div><div><br></div><div>My question is how to ident=
ify which connections / queries from postgres_fdw are generating the `fetch=
 100 from c2` queries, which, in turn, may quite possibly lead to a feature=
 request for having these named uniquely.</div><div><br></div><div>Thanks,<=
/div><div><br></div><div>Colin</div></div><br><div class=3D"gmail_quote gma=
il_quote_container"><div dir=3D"ltr" class=3D"gmail_attr">On Wed, 21 Jan 20=
26 at 16:43, Adrian Klaver &lt;<a href=3D"mailto:adrian.klaver@aklaver.com"=
>adrian.klaver@aklaver.com</a>&gt; wrote:<br></div><blockquote class=3D"gma=
il_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,2=
04,204);padding-left:1ex">On 1/21/26 00:18, Colin &#39;t Hart wrote:<br>
&gt; Hi,<br>
&gt; <br>
&gt; One of my clients makes extensive use of postgres_fdw. After a migrati=
on <br>
&gt; performance isn&#39;t great. pgBadger reports show the slowest queries=
 all <br>
&gt; being `fetch 100 from c2`.<br>
&gt; <br>
&gt; Anyone have any tricks for being able to associate=C2=A0those fetches =
with <br>
&gt; the queries that were used when declaring the server-side cursor?<br>
<br>
This is going to need a lot more information. To start:<br>
<br>
1) Migration of what and from what version to what version?<br>
<br>
2) Where are the Postgres databases relative to each other on the network?<=
br>
<br>
3) What versions of Postgres if not covered in 1.<br>
<br>
4) If Postgres was what was being updated was an analyze done on the <br>
instances?<br>
<br>
5) Show a complete query using EXPLAIN ANALYZE.<br>
<br>
6) Define slow.<br>
<br>
&gt; <br>
&gt; Thanks,<br>
&gt; <br>
&gt; Colin<br>
<br>
<br>
-- <br>
Adrian Klaver<br>
<a href=3D"mailto:adrian.klaver@aklaver.com" target=3D"_blank">adrian.klave=
r@aklaver.com</a><br>
</blockquote></div>

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