LIBRARIES Eternity is a mere moment, just enough for a joke.

The ability to take transaction-consistent snapshots of a distributed persistent object store is useful for online data archive, backup, and recovery. However, most modern snapshot utilities such as those in file systems and database systems are not designed for distributed environments and directly applying these methods to a distributed environment results in poor performance. This thesis describes an efficient snapshot scheme for a distributed persistent object store. Our snapshot scheme provides two basic operations to the users: (1) take a snapshot of the persistent object store and (2) execute a read-only transaction on a previously taken snapshot. Snapshots in our system are based on time. Users take a snapshot by indicating that the snapshot should happen "now " (at the current time). To run a read-only transaction on a snapshot of the system, the user specifies the time in the past at which the transaction should be executed. Our snapshot scheme guarantees serializability with respect to concurrent transactions. It also guarantees external consistency based on the assumption of loosely synchronized clocks among the object stores