While reading [1] in context of Postgres Hibernator, I see that Mitsuru mentioned one of the ways other RDBMS allows count(*) to be driven by an index.
> 'select /*+ INDEX(emp emp_pk) */ count(*) from emp;' to load index blocks I am not sure if Postgres planner already allows this, but it would be great if the planner considered driving a count(*) query using a non-partial index, in the hopes that it turns into an index-only scan, and hence returns count(*) result faster.The non-partial index may not necessarily be the primary key index, it can be chosen purely based on size, favouring smaller indexes. This may alleviate some of the concerns of people migrating applications from other DBMS' that perform count(*) in a blink of an eye. [1]: http://www.postgresql.org/message-id/20110507.022228.83883502.iwas...@jp.freebsd.org Best regards, PS: Please note that I am not proposing to add support for the optimizer hint embedded in Mitsuru's query. -- Gurjeet Singh http://gurjeet.singh.im/ EDB www.EnterpriseDB.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
