Nedyalko Borisov Sandeep Uttamchandani Ramani Routray Aameek Singh Why Did My Query Slow Down. 2009 CIDR http://www-db.cs.wisc.edu/cidr/cidr2009/Paper_72.pdf conf/cidr/2009 db/conf/cidr/cidr2009.html#BorisovURS09