We have a big database with many queries. I optimized one 2 minute
query by adding an index on an integer. The query now takes 2 to 3
seconds.
Another Query however that uses the same table now freezes when this
new index is enabled.
I have had this on 2 different indexing situations.
The plan that was being used with the new index included the new
index when it did not need it because when it was disabled it went
fine.
Does anyone know what would cause this. It makes it impossible to
optimize cause I might kill some other query somewhere in the system.

Thanks.