On Wed, 13 Aug 2003, Lufkin, Brad wrote:
> I'm running the following query:
>
> SELECT * FROM someTable LIMIT 20
>
> I turned on explain analyze (tip #8!) and was told that the query plan was
> sequential (no surprise there) with an estimated cost of between 0.00 and
> 1.07. Surprisingly, the actual time was around 90000 msec (or one-and-a-half
> minutes). What's going on?
costs are estimated as a percentage of a cost of a single page access in
sequential mode. I.e. a single sequential page access is assumed to cost
1.0, and everything is relative to that. The cost numbers do NOT
translate directly into any time unit.