Exo-Leasing: Escrow Synchronization for Mobile Clients of Commodity Storage Servers

Escrow reservations is a well-known synchronization technique, useful for inventory control, that avoids conflicts by taking into account the semantics of fragmentable object types. Unfortunately, current escrow techniques cannot be used on generic “commodity” servers because they require the servers to run the type-specific synchronization code. This is a severe limitation for systems that require applicationspecific synchronization but need to rely on generic components. Our exo-leasing method provides a new way to implement escrow synchronization without running any type-specific code in the servers. Instead, escrow synchronization code runs in the client providing the ability to use commodity servers. Running synchronization code in the client provides an additional benefit. Unlike any other system, our system allows a disconnected client to obtain escrow reservation from another disconnected client, reducing the need to coordinate with the servers. Measurements of a prototype indicate that our approach provides escrowbased conflict avoidance at moderate performance overhead.