Opportunistic peer-to-peer synchronization in a synchronization system

The present invention provides an opportunistic peer-to-peer synchronization method, where client devices can either synchronize with a peer device or a master server, depending on which is the best available option. Client devices monitor synchronization information provided by peer client devices to determine if data that the client device desires to synchronize can be synchronized with a peer client device. If a peer device is available for synchronization, then a client device will synchronize with such peer device. Otherwise, the client device will synchronize with the master server or other device. Client devices can seamlessly switch between peer-to-peer synchronization and client-server synchronization, even during the middle of synchronization session.