Re:

On Mar 6, 2007, at 11:40 AM, Tom Lane wrote:

> the *actual* average number of rows scanned is 3773.  I'm not sure why
> this should be --- is it possible that the distribution of keys in
> symptom_reports is wildly uneven?  This could happen if all of the
> physically earlier rows in symptom_reports contain the same small set
> of symptom_ids, but the stats don't seem to indicate such a skew.

Hi Tom, you are correct, the distribution is uneven... In the 13k  
symptom_reports rows, there are 105 distinct symptom_ids.   But the  
first 8k symptom_reports rows only have 10 distinct symptom_ids.    
Could this cause the problem and would there be anything I could do  
to address it?

Thanks for all your help, I appreciate it.

-Jeff