From: Tom Lane <tgl@sss.pgh.pa.us>
To: aless.jeant@gmail.com
cc: pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #17693: Slow performance: Much slower queries on
 pg_stat_all_tables since 13.4
In-reply-to: <17693-8d263aff1ffe112f@postgresql.org>
References: <17693-8d263aff1ffe112f@postgresql.org>
Comments: In-reply-to PG Bug reporting form <noreply@postgresql.org>
	message dated "Wed, 23 Nov 2022 14:46:47 +0000"
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Date: Wed, 23 Nov 2022 11:41:48 -0500
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PG Bug reporting form <noreply@postgresql.org> writes:
> We did a point upgrade through RDS's managed service which went from 13.4 to
> 13.7. (13.9 is unavailable and we have yet to upgrade to 13.8 - however I
> couldn't find any documentation or issue history reporting similar symptoms
> in the past year of discussions here)

> This created a weird bug which is causing a lot of strain on our systems,
> because we currently run a lot of queries over the pg_stat_all_tables, in
> order to choose candidate tables most appropriate to vacuum preemptively in
> a production system (we have a lot of active tables, order of magnitude 100k
> tables)

> Before this, queries would take <<1 second, now they're always ~5 seconds,
> regardless of what we are filtering on.

RDS is not Postgres; the underlying storage engine is completely
different, as a consequence of which the Postgres layer is pretty
heavily modified (or so we in the community assume, having never
seen any of their source code).  I think you need to take this up
with Amazon.

Just to check, I did create a database with 100K tables in community
Postgres 13.9, and I didn't see any odd behavior with selecting from
pg_stat_all_tables.

			regards, tom lane