Re: 8.1 count(*) distinct: IndexScan/SeqScan

Tom Lane wrote:

>What "same result"? You only ran it up to 2K rows, not 2M. In any
>case, EXPLAIN without ANALYZE is pretty poor ammunition for complaining
>that the planner made the wrong choice. I ran the same
>

Hello, sorry to jump in mid-stream, but this reminded me of something.

I have hit cases where I have a query for which there is a somewhat
"obvious" (to a human...) query plan that should make it possible to get
a query answer pretty quickly. Yet the query "never" finishes (or
rather, after hours of waiting I finally kill it). I assume this is
because of a sub-optimal query plan. But, it appears that an EXPLAIN
ANALYZE runs the actual query, so it takes as long as the actual query.

In such a case, how can I go about tracking down the issue, up to an
including a complaint about the query planner? :-)

(Overall, I'm pretty pleased with the PG query planner; it often gets
better results than another, popular commercial DBMS we use here....
that is just a general impression, not the result of setting up the same
schema in each for a comparison.)

Kyle Cordes
www.kylecordes.com