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Subject: Re: Query runs on 9.2, but not on 9.4
From: Scott Ribe <scott_ribe@elevated-dev.com>
In-Reply-To: 
 <CABzCKRByML4pr5cW373d0vNm-rN-hrt+eda97i2fnEA75qi5HQ@mail.gmail.com>
Date: Wed, 5 Aug 2015 08:16:40 -0600
Cc: "pgsql-admin@postgresql.org" <pgsql-admin@postgresql.org>
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Message-Id: <26BEAB1A-1F90-4850-AE95-99E9CA1CDD37@elevated-dev.com>
References: 
 <CABzCKRByML4pr5cW373d0vNm-rN-hrt+eda97i2fnEA75qi5HQ@mail.gmail.com>
To: John Scalia <jayknowsunix@gmail.com>
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Sender: pgsql-admin-owner@postgresql.org

On Aug 5, 2015, at 7:56 AM, John Scalia <jayknowsunix@gmail.com> wrote:
>=20
> SELECT
> c.relname,
> pg_size_pretty(count(*) * 8192) as buffered,
> round(100.0 * count(*) /
> (SELECT setting FROM pg_settings
> WHERE name=3D'shared_buffers')::integer,1)
> AS buffers_percent,
> round(100.0 * count(*) * 8192 /
> pg_relation_size(c.oid),1)
> AS percent_of_relation
> FROM pg_class c
> INNER JOIN pg_buffercache b
> ON b.relfilenode =3D c.relfilenode
> INNER JOIN pg_database d
> ON (b.reldatabase =3D d.oid AND d.datname =3D current_database())
> GROUP BY c.oid,c.relname
> ORDER BY 3 DESC
> LIMIT 25;

So, the first thing I would do is change:

> round(100.0 * count(*) /
> (SELECT setting FROM pg_settings
> WHERE name=3D'shared_buffers')::integer,1)

to:

> (SELECT setting FROM pg_settings
> WHERE name=3D'shared_buffers')::integer,1)

and change:

> round(100.0 * count(*) * 8192 /
> pg_relation_size(c.oid),1)

to:

> pg_relation_size(c.oid),1)

Then look for 0s in those output columns. I'll bet that the 9.4 vs 9.2 diff=
erence is simply a value of 0 for one of those, not some exotic thing about=
 the query plan. If I'm right about that, then you can start hunting down a=
 specific explanation.

--=20
Scott Ribe
scott_ribe@elevated-dev.com
http://www.elevated-dev.com/
https://www.linkedin.com/in/scottribe/
(303) 722-0567 voice


--=20
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