From: Tom Lane <tgl@sss.pgh.pa.us>
To: John Scalia <jayknowsunix@gmail.com>
cc: "pgsql-admin@postgresql.org" <pgsql-admin@postgresql.org>
Subject: Re: Query runs on 9.2, but not on 9.4
In-reply-to: 
 <CABzCKRByML4pr5cW373d0vNm-rN-hrt+eda97i2fnEA75qi5HQ@mail.gmail.com>
References: 
 <CABzCKRByML4pr5cW373d0vNm-rN-hrt+eda97i2fnEA75qi5HQ@mail.gmail.com>
Comments: In-reply-to John Scalia <jayknowsunix@gmail.com>
 message dated "Wed, 05 Aug 2015 08:56:02 -0500"
Date: Wed, 05 Aug 2015 10:17:55 -0400
Message-ID: <9874.1438784275@sss.pgh.pa.us>
Precedence: bulk
Sender: pgsql-admin-owner@postgresql.org

John Scalia <jayknowsunix@gmail.com> writes:
> I've got a query I use to show the amount of shared buffers in use that is
> giving me some issues. It uses the pg_buffercache extension. The query is:

> SELECT
> c.relname,
> pg_size_pretty(count(*) * 8192) as buffered,
> round(100.0 * count(*) /
> (SELECT setting FROM pg_settings
> WHERE name='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 = c.relfilenode
> INNER JOIN pg_database d
> ON (b.reldatabase = d.oid AND d.datname = current_database())
> GROUP BY c.oid,c.relname
> ORDER BY 3 DESC
> LIMIT 25;

> On a 9.2 system, it runs fine and produces a list of the top 25 tables
> using the shared buffer, but on 9.3 and above, it throw a "division by
> zero" error.

It seems likely that you have at least one table in the 9.4 system for
which pg_relation_size() produces 0, but on the 9.2 system that table is
not there or is not physically zero-length.

			regards, tom lane


-- 
Sent via pgsql-admin mailing list (pgsql-admin@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-admin