Re: slow bitmap heap scans on pg 9.2

On 13-04-10 09:56 AM, ktm@rice.edu wrote:
> On Wed, Apr 10, 2013 at 09:49:55AM -0400, Steve Singer wrote:

>
> Hi Steve,
>
> The one thing that stands out to me is that you are working with 200GB of
> data on a machine with 4-8GB of ram and you have the random_page_cost set
> to 2.0. That is almost completely uncached and I would expect a value of
> 10 or more to be closer to reality.

Setting random_page_cost to 15 makes the planner choose the nested-loop
plan (at least the date range I tried).

I thought that the point of effective cache size was to tell the planner
high likely it is for a random page to be in cache.  With 200GB of data
for this query and an effective cache size of 3.5 GB I would have
expected that to be accounted for.



>
> Regards,
> Ken
>
>