On 9/28/16 1:11 PM, Jake Nielsen wrote:
Beautiful! After changing the random_page_cost to 1.0 the original query went from ~3.5s to ~35ms. This is exactly the kind of insight I was fishing for in the original post. I'll keep in mind that the query planner is very tunable and has these sorts of hardware-related trade-offs in the future. I can't thank you enough!
Be careful with setting random_page_cost to exactly 1... that tells the planner that an index scan has nearly the same cost as a sequential scan, which is absolutely never the case, even with the database in memory. 1.1 or maybe even 1.01 is probably a safer bet.
Also note that you can set those parameters within a single session, as well as within a single transaction. So if you need to force a different setting for a single query, you could always do
BEGIN; SET LOCAL random_page_cost = 1; SELECT ... COMMIT; (or rollback...) -- Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX Experts in Analytics, Data Architecture and PostgreSQL Data in Trouble? Get it in Treble! http://BlueTreble.com 855-TREBLE2 (855-873-2532) mobile: 512-569-9461 -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
