Parameter sniffing is a good thing: it is used by the Query Optimizer to produce an execution plan tailored to the current parameters of a query. However, due to the way that the plan cache stores these plans in memory, sometimes can also be a performance problem. This session will show you how parameter sniffing works and in which cases could be a problem. How to diagnose and troubleshoot parameter sniffing problems and their solutions will be discussed as well. The session will also include details on how the Query Optimizer uses the histogram and density components of the statistics object and some other advanced topics.