Re: pg_relation_size performance issue

Hans Guijt <hg(at)terma(dot)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'm attempting 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