While \"No one size fits all\" is a sound philosophy for system designers to follow, it poses multiple challenges for application developers and system administrators. It can be hard for an application developer to pick one system when the needs of her application match the features of multiple \"One size\" systems. The choice becomes considerably harder when different components of an application fit the features of different \"One size\" systems. Considerable manual effort goes into creating and tuning such multi-system applications. An application's data and workload properties may change over time, often in unpredictable and bursty ways. Consequently, the \"One size\" system that is best for an application can change over time.