From: Jerry Sievers <gsievers19@comcast.net>
To: Luis <luisico@gmail.com>
Cc: pgsql-admin@postgresql.org
Subject: Re: Difference in the size of database size and relations
References: 
 <CAM-gcbSfTp6co+vo5s6UMy4b9oGf9yLFZX9WJKrBR1=P8BoXzw@mail.gmail.com>
Date: Tue, 10 Dec 2013 12:07:59 -0600
In-Reply-To: 
 <CAM-gcbSfTp6co+vo5s6UMy4b9oGf9yLFZX9WJKrBR1=P8BoXzw@mail.gmail.com>
 (Luis's message of "Tue, 10 Dec 2013 12:33:50 +0100")
Message-ID: <86vbyw1sw0.fsf@jerry.enova.com>
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Luis <luisico@gmail.com> writes:

> Hi,
>
> I have noticed a weird thing in different databases.
> When I run pg_database_size on some databases they report a pretty
> high value and if I take a look to all relations the sum of all of
> them is not even the half of the one reported by pg_database_size.
>
> Although I've seen this in different databases, this is a specific example.
>
>
> This are the sizes reported by this query:
>
> SELECT pg_size_pretty(pg_relation_size(C.oid)) AS "size"
>   FROM pg_class C
>   LEFT JOIN pg_namespace N ON (N.oid = C.relnamespace)
>   WHERE nspname NOT IN ('pg_catalog', 'information_schema')
>   ORDER BY pg_relation_size(C.oid) DESC
>   LIMIT 20;
>

Try just comparing what pg_database_size() tells you vs a sum() over
relpages*8192 (assuming standard page size).  You may have to do some
casting to bigint depending how large your DB is.

>   size
> ---------
>  99 MB
>  45 MB
>  10 MB
>  8528 kB
>  5280 kB
>  4352 kB
>  3184 kB
>  1304 kB
>  1152 kB
>  896 kB
>  544 kB
>  528 kB
>  336 kB
>  336 kB
>  336 kB
>  304 kB
>  296 kB
>  288 kB
>  272 kB
>  248 kB
>
> And this is the database size reported by this query:
> SELECT pg_size_pretty(pg_database_size('mydb'));
>
>  pg_size_pretty
> ----------------
>  3539 MB
>
> I've read about LOBs but I don't seem to have any.
>
> Any idea where the space is being used?
>
> Thanks

-- 
Jerry Sievers
Postgres DBA/Development Consulting
e: postgres.consulting@comcast.net
p: 312.241.7800


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