The DeltaManager manages replicated sessions by only replicating the deltas in data. For applications written to handle this, the DeltaManager is the optimal way of replicating data. This code is almost identical to StandardManager with a difference in how it persists sessions and some modifications to it. IMPLEMENTATION NOTE : Correct behavior of session storing and reloading depends upon external calls to the start() and stop() methods of this class at the correct times.