On Sat, Jun 22, 2013 at 9:48 AM, Stephen Frost <sfr...@snowman.net> wrote: >> The correct calculation that would match the objective set out in the >> comment would be >> >> dbuckets = (hash_table_bytes / tupsize) / NTUP_PER_BUCKET; > > This looks to be driving the size of the hash table size off of "how > many of this size tuple can I fit into memory?" and ignoring how many > actual rows we have to hash. Consider a work_mem of 1GB with a small > number of rows to actually hash- say 50. With a tupsize of 8 bytes, > we'd be creating a hash table sized for some 13M buckets.
This is a fair point, but I still think Simon's got a good point, too. Letting the number of buckets ramp up when there's ample memory seems like a broadly sensible strategy. We might need to put a floor on the effective load factor, though. -- 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
