Re: Trying to figure out why these queries are so slow

Hi,

just a guess: Counting is slow, since it needs to check all rows. Explained here:

http://wiki.postgresql.org/wiki/Slow_Counting

Thomas Güttler

Tim Uckun wrote:
> I have two tables. Table C has about 300K records in it. Table E has
> about a million records in it. Today I tried to run this query.
>
> update C
> set result_count = X.result_count
> from C
> inner join (select c_id, count(c_id) as result_count
> from E
> where c_id is not null
> group by c_id) as X
> on C.id = X.c_id
>
> All the fields mentioned are indexed. In the case of Table C it's the
> primary key. In the case table E it's just an index (non unique).
>
> I let this query run for about three hours before I cancelled it.
> ...

--
Thomas Guettler, http://www.thomas-guettler.de/
E-Mail: guettli (*) thomas-guettler + de