Performance -- Plan Cost and Scan

I am looking some query stats and have a query.
Query 1 Plan Cost: 5.312 -- Execution 20.497 seconds -- total time 23.848
seconds --Physical Reads 1,404, Logical Reads, 927,701,Scans 621, Read Ahead
Reads - 3,976
Query 2 Plan Cost 9.469 -- Exection 00.143 seconds -- total time 02.016
seconds -- physical reads 0, logical reads 7146, sans 622 , read ahead reads
100
Query 2 obviously runs around 95% faster and it would seem difference
between plan cost is very little.
What is the downside of having the plan cost go up? Under heavier load
would this start to perform poorly because of that? At what point does the
plan cost become more important than the other items? Or are the logical
reads a better indiciator of which way to go.
Sorry for so many questions -- really starting to use the tools to tweak
queries and want to make sure I am going down right paths.
Thanks!!!Execution plan costs are worth looking at, but must be taken with a
bit of skepticism. The cost in the execution plan is just an
estimate. The actual results can be quite different. You can even
get completely different execution plans sometimes just by updating
statistics.
Roy Harvey
Beacon Falls, CT
On Tue, 28 Feb 2006 10:46:07 -0500, "Brian" <brian@.nospam.com> wrote:

>I am looking some query stats and have a query.
>Query 1 Plan Cost: 5.312 -- Execution 20.497 seconds -- total time 23.848
>seconds --Physical Reads 1,404, Logical Reads, 927,701,Scans 621, Read Ahea
d
>Reads - 3,976
>Query 2 Plan Cost 9.469 -- Exection 00.143 seconds -- total time 02.016
>seconds -- physical reads 0, logical reads 7146, sans 622 , read ahead read
s
>100
>
>Query 2 obviously runs around 95% faster and it would seem difference
>between plan cost is very little.
>What is the downside of having the plan cost go up? Under heavier load
>would this start to perform poorly because of that? At what point does the
>plan cost become more important than the other items? Or are the logical
>reads a better indiciator of which way to go.
>Sorry for so many questions -- really starting to use the tools to tweak
>queries and want to make sure I am going down right paths.
>Thanks!!!
>