=?UTF-8?Q?Grzegorz_Ja=C5=9Bkiewicz?= <gryzman@xxxxxxxxx> writes: > On Thu, Feb 12, 2009 at 1:10 PM, Rory Campbell-Lange > <rory@xxxxxxxxxxxxxxxxxx> wrote: >> UPDATE >> users >> SET t_firstname = >> (select firstname from testnames order by random() limit 1), >> t_surname = >> (select lastname from testnames order by random() limit 1) >> WHERE >> n_role IN (2,3); >> >> Doesn't return either after 60 seconds on a 8 core machine with 8GB of >> RAM and 15K disks in R10 (no swap in use). > That would be because, for every row in users table, postgres has to > run two subselects, with order by random() (which in it self is quite > expensive). Well, no, because those subselects are independent of the parent query; I'd expect PG to do them just once. Do they show up as "SubPlans" or "InitPlans" in EXPLAIN? regards, tom lane -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
