Re: Query Time

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.