Date: Wed, 20 Jun 2018 18:42:03 -0400
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Wells Oliver <wells.oliver@gmail.com>
Cc: pgsql-admin <pgsql-admin@postgresql.org>
Subject: Re: explaining the pg_total_relation_size/pg_relation_size results
Message-ID: <20180620224203.fqlzl2d3dhvcbe7q@alvherre.pgsql>
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On 2018-Jun-20, Wells Oliver wrote:

> I have the follwing in a view to glance at the size of my relations:
> 
> pg_size_pretty(pg_relation_size(c.oid::regclass)) AS size,
> pg_total_relation_size(c.oid::regclass) AS bytes
> 
> This view sorts by pg_relation_size(c.oid::regclass) descending.
> 
> The question is: the byte values are often higher for relations with a
> lower size indicated by size. As I sit here, I see an 11GB table
> of 23821893632 bytes and a 12GB table of 14545387520 bytes, and
> lastly/weirdly, a 3194MB table of 19924844544 bytes.

This is a strange question.  pg_total_relation_size includes the size of
indexes and toast table and index, which pg_relation_size does not, so
it seems natural that they give wildly different results for differently
shaped tables.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services