Quorum-based synchronization protocols for multimedia replicas

摘要

Multiple replicas of multimedia objects are distributed to peers in overlay networks. In quorum-based (QB) protocols, every replica may not be up-to-date and the upto-date replica can be found in the version counter. Multimedia objects are characterized in terms of not only data structure but also quality of service (QoS) parameters like frame rate. A transaction reads a parameter of a replica while there is a type of read operation to read a whole state of a replica. Each parameter of a replica is changed through a write operation. Thus, the data structure and QoS parameters of a replica are independently manipulated. In the multimedia quorum-based (MQB) protocol, multiple replicas of a multimedia object are synchronized based on the newness precedent relation. An object is an encapsulation of data and abstract operations for manipulating the data. There are enriching and impoverishing types of write operations. Some data is added to a replica in an enriching operation. On the other hand, some data in a replica is removed in an impoverishing operation. In order to reduce the overhead to write every replica in a quorum, we take an approach that the state of each replica is not always updated. If a transaction issues an enriching write operation, every replica in the write quorum is updated in the same way as the QB protocol. On the other hand, if an impoverishing write operation is issued, every replica is not updated in the quorum. Impoverishing operations are just recorded in replicas. On receipt of a read operation to read a whole state, impoverishing operations recorded are performed on a replica. The MQB protocol is evaluated in terms of the processing overhead of replicas. We show that the processing overhead of each replica can be reduced in the MQB protocol.