On Tue, Dec 4, 2012 at 12:06 PM, <postgresql@foo.me.uk> wrote:
> Slow version with bitmapscan enabled: http://explain.depesz.com/s/6I7
> Fast version with bitmapscan disabled: http://explain.depesz.com/s/4MWG
If you check the "fast" plan, it has a higher cost compared against
the "slow" plan.
The difference between cost estimation and actual cost of your
queries, under relatively precise row estimates, seems to suggest your
e_c_s or r_p_c aren't a reflection of your hardware's performance.
First, make sure caching isn't interfering with your results. Run each
query several times.
Then, if the difference persists, you may have to tweak
effective_cache_size first, maybe random_page_cost too, to better
match your I/O subsystem's actual performance
