From: Tom Lane <tgl@sss.pgh.pa.us>
To: Lars Aksel Opsahl <Lars.Opsahl@nibio.no>
cc: Vijaykumar Jain <vijaykumarjain.github@gmail.com>,
        Pgsql Performance <pgsql-performance@lists.postgresql.org>
Subject: Re: slow "select count(*) from information_schema.tables;" in some
 cases
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Comments: In-reply-to Lars Aksel Opsahl <Lars.Opsahl@nibio.no>
	message dated "Mon, 07 Feb 2022 18:55:57 +0000"
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Date: Mon, 07 Feb 2022 14:02:50 -0500
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Lars Aksel Opsahl <Lars.Opsahl@nibio.no> writes:
>> SELECT relname, pg_size_pretty(pg_relation_size(C.oid)) FROM pg_class C=
 LEFT JOIN pg_namespace N ON (N.oid =3D C.relnamespace) WHERE nspname =3D =
'pg_catalog' ORDER BY 2 DESC LIMIT 20; can you show the output of this que=
ry

"ORDER BY 2" is giving you a textual sort of the sizes, which is entirely
unhelpful.  Try

SELECT relname, pg_size_pretty(pg_relation_size(C.oid)) FROM pg_class C LE=
FT JOIN pg_namespace N ON (N.oid =3D C.relnamespace) WHERE nspname =3D 'pg=
_catalog' ORDER BY pg_relation_size(C.oid) DESC LIMIT 20;

			regards, tom lane