Re: query planner weirdness?

"Bob Duffey" <bobduffey68@gmail.com> writes:
> 2008/6/28 Steve Atkins <steve@blighty.com>:
>> If you're iterating through the records with a cursor, the plan may
>> be different, IIRC - weighted to provide first row quickly, as opposed
>> to the query that was run that's weighted to provide last row quickly.
>>
> I agree, and I was hoping that would be the case, but as it happens it
> wasn't.

The planner does in fact pay more attention to first-row cost than total
cost when given a DECLARE CURSOR instead of a regular SELECT.
Apparently that wasn't enough to make the indexscan be preferred,
though, which is a bit curious.  You might want to look at
effective_cache_size as well as random_page_cost.

            regards, tom lane