Selectivity estimation error is one of the main cause of bad query plans. It’s quite straighforward to compute those estimation error using EXPLAIN (ANALYZE), either manually or with the help of explain.depesz.com (or other similar tools), but until now there were now tool available to get this information automatically and globally. Version 2 of pg_qualstats fixes that, thanks a lot to Oleg Bartunov for the original idea!
