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Posted by wizofaus on 01/11/07 10:04
Uri Dimant wrote:
> Hi
> http://blogs.msdn.com/khen1234/archive/2005/06/02/424228.aspx
>
Thanks for that...amazingly enough it turned that that was exactly my
problem, although I'm using ad-hoc queries rather than stored procs. I
did some more testing, and it turned out that it was because it was
executing the same query twice, the first time with an atypical
parameter value, and the second time with a more typical one, that the
query was running so slowly. That is, executing
SELECT Min(MyValue) FROM MyTable WHERE MyKey = @0, with @0 = 999
followed by
SELECT Min(MyValue) FROM MyTable WHERE MyKey = @0, with @0 = 123
Caused the second query to run absurdly slowly, because in the first
case only very few rows in the table had MyKey = 999 whereas almost
every row had MyKey = 123. After doing a DBCC FREEPROCCACHE and
swapping the queries around, they both ran fine.
In the end I ended up de-parameterizing the query just for this case,
but now I'm worried - how can I be sure that my other queries won't
suffer from the same problem? Should I never use parameters because of
this possibility?
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