"Robert Haas" <robertmhaas@xxxxxxxxx> writes: >> What's strange about it? A probe into an in-memory hashtable is a lot >> cheaper than a probe into an index, so this type of plan makes plenty >> of sense if the hashtable will fit in RAM and there are going to be a >> lot of probes. (Where "a lot" means "enough to amortize the cost of >> building the hashtable", of course.) > Hmm... it didn't occur to me that the index probe itself might be > more expensive than a hash probe. Is that due to concurrency control, > or are you talking about the need to possibly read index pages in from > disk? Both, plus the loss of sequentiality of access to the table itself. >>> Experimentation shows this is actually about 25% faster. >> >> Well, that just says your cost parameters need a bit of adjustment >> if you'd like the planner to get the crossover point exactly right. > Any sense of which ones might be worth fiddling with? random_page_cost, effective_cache_size, maybe the cpu_xxx parameters. regards, tom lane -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
