"Kevin Grittner" <kevin.gritt...@wicourts.gov> writes: > Bruce Momjian <br...@momjian.us> wrote: >> I talked to Robert Haas and he said that index-only scans do not >> optimize COUNT(*). Is this something we can do for PG 9.2? Is >> anyone working on this? > Well, it's not that it doesn't optimize COUNT(*) -- it's that it > doesn't yet cost the index scan as cheaper than a table scan when > you're accessing every row.
I think what Robert is complaining about is that we won't currently consider an index that matches neither any WHERE clauses nor ORDER BY, ie, count(*) over the whole table won't get considered for an index-only scan, regardless of cost estimates. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers