Re: pg_relation_size performance issue

Hans Guijt <hg@terma.com> writes:
> I have a Postgres 9.3.7 database, freshly created on Ubuntu 14 LTS 64 bit, and at this time almost completely empty.
I'mattempting to find the size of a table, using the following code: 
> SELECT
>   pg_relation_size (stat.relid),
>   CASE WHEN cl.reltoastrelid = 0 THEN
>   0
>   ELSE
>   pg_relation_size (cl.reltoastrelid) + COALESCE ((
>   SELECT SUM (pg_relation_size (indexrelid)) FROM pg_index WHERE indrelid=cl.reltoastrelid
>   ), 0)::int8
> END,
> COALESCE ((SELECT SUM (pg_relation_size (indexrelid)) FROM pg_index WHERE indrelid=stat.relid), 0)::int8
> FROM pg_stat_all_tables stat
> JOIN pg_class cl ON cl.oid=stat.relid
> JOIN pg_namespace ns ON cl.relnamespace=ns.oid
> WHERE UPPER (cl.relname) = UPPER ('sensor')
>    AND UPPER (ns.nspname) = UPPER ('devtest')

Getting rid of the useless join to pg_stat_all_tables would probably help;
there's a lot of computation in that view.

            regards, tom lane