LIMIT 65536; Total query runtime: 14846 ms. - http://explain.depesz.com/s/I3E LIMIT 69632: Total query runtime: 80141 ms. - http://explain.depesz.com/s/9hp
So it looks like when the limit crosses a certain threshold (somewhere north of 2^16), Postgres decides to do a Seq Scan instead of an Index Scan. I've already lowered random_page_cost to 2. Maybe I should lower it to 1.5? Actually 60K should be plenty for my purposes anyway. On Wed, Feb 1, 2012 at 10:35 AM, Scott Marlowe <scott.marl...@gmail.com>wrote: > On Wed, Feb 1, 2012 at 11:19 AM, Alessandro Gagliardi > <alessan...@path.com> wrote: > > Interestingly, increasing the limit does not seem to increase the > runtime in > > a linear fashion. When I run it with a limit of 60000 I get a runtime > > of 14991 ms. But if I run it with a limit of 70000 I get a runtime > of 77744 > > ms. I assume that that's because I'm hitting a memory limit and paging > out. > > Is that right? > > Hard to say. more likely your query plan changes at that point. Run > the queries with "explain analyze" in front of them to find out. >
