Completable Quorums of Multimedia Objects

Multimedia objects are distributed to peers through downloading and caching in peer-to-peer (P2P) overlay networks. In the quorum-based (QB) protocols, every replica of an object is not up-to-date and the replicas are totally ordered in the version counters. On the other hand, multimedia objects are characterized in terms of not only data structure but also quality of service (QoS) like number of colours. Replicas of a multimedia object are partially ordered in terms of the newness precedent relation on not only data structure but also QoS. An object is an encapsulation of data structure and abstract operations for manipulating the data structure. Operations are classified into write (W), read (R), and read-write (RW) types. An object is changed though two types of W/RW operations, enriching and impoverishing types. 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 every replica is not updated. If a transaction issues an enriching operation, every replica in the quorum is updated in the same way as the QB protocol. On the other hand, if an impoverishing type of write operation is issued, every replica is not updated in the quorum. Impoverishing operations are logged in replicas while enriching operations are performed on every replica. Then, impoverishing operations in a log are later performed on a replica.