ach <alanchines@xxxxxxxxx> wrote: > One quick follow up since I'm expecting y'all might know: Do the > statistics targets actually speed performance on an index search > itself; the actual lookup? Or are the JUST to inform the planner > towards the best pathway decision? Since the statistics are just a random sampling and generally not completely up-to-date, they really can't be used for anything other than *estimating* relative costs in order to try to pick the best plan. Once a plan is chosen, its execution time is not influenced by the statistics. A higher statistics target can increase planning time. In a complex query with many joins and many indexes on the referenced tables, the increase in planning time can be significant. I have seen cases where blindly increasing the default statistics target resulted in planning time which was longer than run time -- without any increase in plan quality. Generally when something is configurable, it's because there can be benefit to adjusting it. If there was a single setting which could not be materially improved upon for some cases, we wouldn't expose a configuration option. This is something which is not only globally adjustable, you can override the setting for individual columns -- again, we don't go to the trouble of supporting that without a good reason. -- Kevin Grittner 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
