On Mon, Apr 1, 2013 at 2:35 AM, Jeff Davis <pg...@j-davis.com> wrote: > On Sun, 2013-03-31 at 15:45 -0400, Tom Lane wrote: >> Really, when we're traipsing down a bucket >> list, skipping over bucket entries with the wrong hash code is just >> about free, or at least it's a whole lot cheaper than applying ExecQual. >> >> Perhaps what we should do is charge the hash_qual_cost only for some >> small multiple of the number of tuples that we expect will *pass* the >> hash quals, which is a number we have to compute anyway. The multiple >> would represent the rate of hash-code collisions we expect. > > +1. > >> I'd still be inclined to charge something per bucket entry, but it >> should be really small, perhaps on the order of 0.01 times >> cpu_operator_cost. > >> Or we could just drop that term entirely. > > FWIW, either of those are fine with me based on my limited experience.
FWIW, I have also seen this problem and the proposed fixes sound reasonable to me. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
