Robert Haas <robertmhaas@xxxxxxxxx> writes: > On Thu, Jan 13, 2011 at 3:12 PM, Jon Nelson <jnelson+pgsql@xxxxxxxxxxx> wrote: >> I still think that having UNION do de-duplication of each contributory >> relation is a beneficial thing to consider -- especially if postgresql >> thinks the uniqueness is not very high. > This might be worth a TODO. I don't believe there is any case where hashing each individual relation is a win compared to hashing them all together. If the optimizer were smart enough to be considering the situation as a whole, it would always do the latter. regards, tom lane -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
