Greg Stark wrote: > On Wed, May 11, 2011 at 1:47 AM, Bruce Momjian <br...@momjian.us> wrote: > > Isn't speeding up COUNT(*) a sufficient case because it will not have to > > touch the heap in many cases? > > Putting aside the politics questions, count(*) is an interesting case > -- it exposes some of the unanswered questions about index-only scans. > > The reason "select count(*)" might win would be because we could pick > any index and do an index scan, relying on the visibility map to > optimize away the heap reads. This is only going to be a win if a > large fraction of the heap reads get optimized away. > > It's going to be pretty tricky to determine in the optimizer a) which > index will be cheapest and b) what fraction of index tuples will point
I assume the smallest non-partial index would be the cheapest index. -- Bruce Momjian <br...@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + It's impossible for everything to be true. + -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
