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help / color / mirror / Atom feedFrom: Ron Johnson <[email protected]>
To: pgsql-admin <[email protected]>
Subject: pg_stats.correlation rule of thumb for re-clustering a table?
Date: Fri, 12 Sep 2025 10:46:30 -0400
Message-ID: <CANzqJaCEvOm_zY7Ex_vN3r5cQLzWx9DxYd3hV=pwPmm4wsJGWQ@mail.gmail.com> (raw)
(By re-cluster, I of course mean pg_repack.)
Purely OLTP tables (that are only accessed randomly) can of course live
with 0% correlation, but lots of tables are mixed-use, and so benefit from
physical ordering on a carefully chosen field..
SELECT abs(correlation)::numeric(3,2) as correlation
FROM pg_stats
WHERE schemaname = 'foo' AND tablename = 'bar'
AND attname = 'blarge';
correlation
-------------
0.84
(1 row)
Obviously 84% is no need to worry, but what about 60% or 40%? Currently, I
use 60%, but would like to do better.
--
Death to <Redacted>, and butter sauce.
Don't boil me, I'm still alive.
<Redacted> lobster!
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