On Fri, 2002-11-01 at 08:03, mallah(at)trade-india(dot)com wrote:
>
> Hi Rod ,
>
> Does it means that index scan is used for less frequenlty occuring data?
> yes my table was not clustered.
>
> can u tell me what does 0.00..6788.24 and rows and width means?
>
> in explain out put cost=0.00..6788.24 rows=30001 width=4
>
>
> I have one more table where i face the similar problem , i have not dump - reloaded
> it yet , will post again if i face the problem.
Keep in mind that an index scan is very expensive in regards to a single
tuple. It has to run through (fetch) the index pages, then fetch the
pages from the table. Since the table fetches are random, the harddrive
will probably incur a seek for each tuple found in the index. The seeks
add up much quicker than a sequential scan (without nearly as many seeks
or drive head movements).
--
Rod Taylor