On Thu, 2013-03-28 at 19:56 -0400, Stephen Frost wrote: > 41K hashed, seqscan 4M: 115030.10 + 1229.46 = 116259.56 > 4M hashed, seqscan 41K: 1229.46 + 211156.20 = 212385.66
I think those are backwards -- typo? > In the end, I think the problem here is that we are charging far too > much for these bucket costs (particularly when we're getting them so > far wrong) and not nearly enough for the cost of building the hash > table in the first place. > > Thoughts? Ideas about how we can 'fix' this? Have others run into > similar issues? Yes, I have run into this issue (or something very similar). I don't understand why the bucketsize even matters much -- assuming few hash collisions, we are not actually evaluating the quals any more times than necessary. So why all of the hashjoin-specific logic in determining the number of qual evaluations? The only reason I can think of is to model the cost of comparing the hashes themselves. Also, searching the archives turns up at least one other, but I think I've seen more: http://www.postgresql.org/message-id/a82128a6-4e3b-43bd-858d-21b129f7b...@richrelevance.com Regards, Jeff Davis -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
