@aaz, @erictgrubaugh, @alien4u: I ran into this issue two weeks back, and @alien4u, your suggestion is correct, to delete the script deployment will stop the map reduce. If the deployment record cannot be deleted, then you will have to delete the Script record to kill the execution instance.

Thanks @margo for reply... My issue got resolved.. Data was very huge...It does take time for searching data but after search completed it runs smoothly. Thanks everyone