On 22 June 2013 21:40, Stephen Frost <sfr...@snowman.net> wrote: > I'm actually not a huge fan of this as it's certainly not cheap to do. If it > can be shown to be better than an improved heuristic then perhaps it would > work but I'm not convinced.
We need two heuristics, it would seem: * an initial heuristic to overestimate the number of buckets when we have sufficient memory to do so * a heuristic to determine whether it is cheaper to rebuild a dense hash table into a better one. Although I like Heikki's rebuild approach we can't do this every x2 overstretch. Given large underestimates exist we'll end up rehashing 5-12 times, which seems bad. Better to let the hash table build and then re-hash once, it we can see it will be useful. OK? -- Simon Riggs http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
