Reduction of Processing Overhead to Synchronize Multmedia Replicas

摘要

Replicas of a multimedia object are characterized in terms of not only data structure but also quality of service (QoS). Multimedia replicas are updated by two types of write operations, i.e. enriching and impoverishing types, where some data is added and removed in a replica, respectively. Computation resources are spent to materialize, i.e. physically update multimedia replicas by encoding and decoding multimedia data. It is critical to reduce the processing overhead of each replica to materialize. In our protocol named an extended multimedia quorum-based (EMQB) protocol, a replica in a write quorum is not materialized each time a write operation is issued. Only in an enriching type of write operation, some number, not necessarily all of replicas in a write quorum are materialized. In the other replicas, write operations are just logged but not performed. The replica can be materialized by performing operations in the log if every operation is an impoverishing type because just some data in a physical state of the replica is removed. However, the replica cannot be materialized if some operation is an enriching type in the log. Hence, a newest, materialized replica may not be in a read quorum. In the EMQB protocol, replicas are randomly selected to be in a read quorum until a materialized replica is ound. We show that the processing overhead of each replica can be reduced in the EMQB protocol compared with the QB and MQB protocols in terms of the total processing overhead of replicas.