On Fri, May 13, 2011 at 3:20 PM, Tom Lane <tgl@xxxxxxxxxxxxx> wrote: > Robert Haas <robertmhaas@xxxxxxxxx> writes: >> On Tue, Apr 26, 2011 at 9:04 PM, Merlin Moncure <mmoncure@xxxxxxxxx> wrote: >>> The very first thing to check is effective_cache_size and to set it to >>> a reasonable value. > >> Actually, effective_cache_size has no impact on costing except when >> planning a nested loop with inner index scan. So, a query against a >> single table can never benefit from changing that setting. > > That's flat out wrong. It does affect the cost estimate for plain > indexscan (and bitmap indexscan) plans. <rereads code> OK, I agree. I obviously misinterpreted this code the last time I read it. I guess maybe the reason why it didn't matter for the OP is that - if the size of the index page in pages is smaller than the pro-rated fraction of effective_cache_size allowed to the index - then the exact value doesn't affect the answer. I apparently need to study this code more. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
