The authors observe that the increased demand for complex analytics has translated into an increased demand for User-Defined Operations (UDOs) - relational algebra and its close derivatives are not enough. They demonstrate SkewTune, a system that automatically mitigates skew in user-defined MapReduce programs and is a drop-in replacement for Hadoop. The demonstration has two parts. First, they demonstrate how SkewTune mitigates skew in real MapReduce applications at runtime by running a real application in a public cloud. Second, through an interactive graphical interface, they demonstrate the details of the skew mitigation process using both real and synthetic workloads that represent various skew configurations.