Asynchronous Epoch Management in Replicated Databases

The paper describes a new dynamic protocol for managing replicated data. Like the existing dynamic schemes, our protocol involves reconfiguring the system dynamically to reflect failures and repairs as they occur, so that the data may be kept available for user operations even if only one replica of the data remains accessible. However, in the existing schemes, it is required for the correctness of the protocol that the system reconfiguration either run as a special transaction that competes for locks with user operations and thus can interfere with and delay the latter, or be done within the protocol for the write operation, which increases the cost of writes and makes fault tolerance of the system dependent on the rate of write operations. In contrast, our protocol allows system reconfiguration to be done asynchronously with and separately from read and write operations. Therefore, in our protocol, user operations can execute while system reconfiguration is in progress, with no interference. At the same time, the cost of write operations in our protocol remains low and the fault tolerance of the system does not depend on the rate of writes.