On Wed, Jul 30, 2008 at 11:08:06PM -0400, Tom Lane wrote: > Hmm, what have you got work_mem set to? The first one would likely > have been a lot faster if it had hashed the subplan; which I'd have > thought would happen with only 80K rows in the subplan result, > except it didn't.
work_mem = 1024kB The machine has 48 MB total RAM and is a Xen host. > The queries are in fact not exactly equivalent, because EXCEPT > involves some duplicate-elimination behavior that won't happen > in the NOT IN formulation. So I don't apologize for your having > gotten different plans. But if use EXCEPT ALL? > Another issue is that the NOT IN will probably not do what you > expected if the subquery yields any NULLs. In this specific query I think it is not possible for the subquery to have NULLs, because its an INNER JOIN USING (the_only_column_in_the _result, some_other_column_also). If any "uid" column of any row would have been NULL, it wouldn't appear in that INNER JOIN, no? -- Miernik http://miernik.name/ -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
