Re: From Simple to Complex

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(dot)marlowe(at)gmail(dot)com>wrote:

> On Wed, Feb 1, 2012 at 11:19 AM, Alessandro Gagliardi
> <alessandro(at)path(dot)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.
>