Bruce Momjian wrote: > Robert Haas wrote: > > On Wed, Aug 11, 2010 at 9:42 PM, Bruce Momjian <bruce@xxxxxxxxxx> wrote: > > > This confused me. ?If we are assuing the data is in > > > effective_cache_size, why are we adding sequential/random page cost to > > > the query cost routines? > > > > See the comments for index_pages_fetched(). We basically assume that > > all data starts uncached at the beginning of each query - in fact, > > each plan node. effective_cache_size only measures the chances that > > if we hit the same block again later in the execution of something > > like a nested-loop-with-inner-indexscan, it'll still be in cache. > > > > It's an extremely weak knob, and unless you have tables or indices > > that are larger than RAM, the only mistake you can make is setting it > > too low. > > The attached patch documents that there is no assumption that data > remains in the disk cache between queries. I thought this information > might be helpful. Applied. -- Bruce Momjian <bruce@xxxxxxxxxx> http://momjian.us EnterpriseDB http://enterprisedb.com + It's impossible for everything to be true. + -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
