Tadateru Ohkawara

Quorum-Based Replication of Multimedia Objects in Distributed Systems

In information systems, resource objects like databases are distributed and replicated in order to increase the performance, reliability, and availability. Especially, multimedia objects like movies are distributed. In this paper, we consider multimedia objects which are characterized in terms of not only data structure but also quality of service (QoS). Here, a pair of replicas of a movie object may have the same content but different levels of QoS, e.g. fully coloured and monochromatic ones. Thus, kinds of replicas of a multimedia object are distributed to peers in various ways. Replicas of an object are thus partially ordered in terms of newness of contents and QoS. In traditional quorum theories, it is critical to find which replica is the newest in each quorum. In this sense, replicas are totally ordered in terms of newness. On the other hand, the content may be the newest but the QoS may not be the newest in a replica of a multimedia object. Replicas of an object are thus partially ordered in terms of newness of contents and QoS. We newly define a partially ordering relation, newness-precedency of replicas to show which replica is newer than another in terms of content and QoS. We classify operations on an object to types with respect to whether or not a transaction inputs and outputs data in an object. We define a quorum for each operation type of an operation on the basis of the newness-precedent relation. We discuss how to synchronize multiple replicas to make consistent on the basis of the quorum concept.

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.

Quorums-based Replication of Multimedia Objects in Distributed Systems

BackgroundMultimedia objects like music and movies are distributed to peers through downloading and caching in peer-to-peer (P2P) overlay networks. In this paper, we consider multimedia objects which are characterized in terms of not only data structure but also quality of service (QoS) like frame rate and number of colours. For example, there are a pair of replicas oiand ojof a fully coloured movie object o. Here, a content of a replica oiis changed by adding a subobject but another replica ojis not changed. On the other hand, the colour of the replica ojis changed with monochromatic one but not in the replica oi. This means, the replica oiis newer than the replica ojwith respect to the content but is older than ojwith respect to QoS. Thus, replicas of a multimedia object are partially ordered in terms of newness of not only content but also QoS parameters.MethodsIn traditional quorum-based (QB) protocols, replicas are totally ordered just in terms of newness of content. We discuss a multimedia quorum-based (MQB) protocol to synchronize multiple replicas to make consistent on the basis of the newness-precedent relation of replicas. Here, the replicas are ordered in vectors of version counters of content and QoS parameters. Every replica in a quorum is not updated for QoS operations to reduce the communication overhead. We evaluate the MQB protocol in terms of communication overhead and show the communication overhead can be reduced in the MQB protocol compared with the traditional QB protocol.ConclusionsWe discussed the multimedia quorum-based (MQB) protocol to keep replicas of a multimedia object mutually consistent. We evaluated the MQB protocol in terms of the total volume of data transmitted among the replicas. Then, we showed the total amount of data transmitted can be reduced in the MQB protocol compared with the traditional quorum-based (QB) protocol.

Quorums for Replication of Multimedia Objects in P2P Overlay Networks

Replicas of multimedia objects are distributed to peers through downloading and caching in peer-to-peer(P2P) overlay networks. Every replica has to be consistent. In quorum-based (QB) protocols, every replica may not be up-to-date and the up-to-date replicas can be found in the version counters. On the other hand, multimedia objects are characterized in terms of not only data structure parameter but also quality of service (QoS) parameters like frame rates. Replicas of a multimedia object are partially ordered in terms of the newness precedent relation on data structure and QoS. Each parameter of a replica is manipulated in read and write operations. In addition, there is a read operation to read a whole replica. A parameter of an object is changed through a write operation. 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 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 write operation is issued, every replica is not updated in the quorum. Impoverishing operations are just recorded in replicas. Then, impoverishing operations are later performed on a replica. The MQB protocol is evaluated in terms of the processing overhead in replicas.0

Quorum-based synchronization protocols for multimedia replicas

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 up-to-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.

Enriching and Impoverishing Types of Write Operations in the Multimedia Quorum-based (MQB) Protocol

Multimedia objects are distributed to peers through downloading and caching in peer-to-peer (P2P) overlay networks. Multimedia objects are characterized in terms of not only data structure but also quality of service (QoS). Replicas of a multimedia object are partially ordered in terms of newness of data structure and QoS. We discuss the multimedia quorum-based (MQB) protocol to synchronize multiple replicas of a multimedia object. We classify write operations on a multimedia object into enriching and impoverishing types of operations. In an enriching operation, some data is added to a replica like an operation to increase the number of colours. In an impoverishing operation, some data in a replica is removed like operation to degrade QoS. If an enriching operation is issued to replicas, the replicas are updated like traditional quorum-based (QB) protocols. On the other hand, every replica in a quorum is not updated in impoverishing operations to reduce communication and computation overheads. On the other hand, an impoverishing operation is just logged in a replica and is not performed on the replica.

A Quorum-Based Synchronization Protocol

Multimedia objects are distributed to peers through downloading and caching in peer-to-peer (P2P) overlay networks. In this paper, we consider multimedia objects which are characterized in terms of not only data structure but also quality of service (QoS). For example, there are a pair of replicas oi and oj of a movie object. Here, a content of a replica oi is changed while not in another replica oj. On the other hand, QoS of the replica oj is changed while not in oi. This means, oi is newer than oj with respect to the content but is older than oj with respect to QoS. Thus, replicas of a multimedia object are partially ordered in terms of newness of content and QoS. In traditional quorum-based (QB) protocols theories, replicas are totally ordered just in terms of newness of content. We discuss a multimedia quorum-based (MQB) protocol to synchronize multiple replicas to make consistent on the basis of the newness-precedent relation of replicas. We evaluate the MQB protocol in terms of communication overheads and show the communication overhead can be reduced in the MQB protocol compared with the traditional QB protocols.

An Extended Multimedia Quorum-based Synchronization Protocol

We discuss how to efficiently and consistently manipulate multiple replicas of a multimedia object. Multimedia replicas are characterized in terms of not only data structure but also quality of service (QoS). Multimedia replicas are written in enriching and impoverishing types of write operations 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. We discuss an extended multimedia quorum-based (EMQB) protocol to reduce the processing overhead of each replica. Here, a replica is not materialized in an impoverishing type of write operation. Even in an enriching type of write operation, only some number, not necessarily all of replicas in a write quorum are materialized. Hence, a newest, materialized replica may not be in a read quorum. Even if one newest replica is surely found in a read quorum, no newest replica might be materialized and a transaction cannot read any replica. In the EMQB protocol, replicas are randomly selected to be in a read quorum until a materialized replica is found. The EMQB protocol is evaluated in terms of the total processing overhead of replicas compared with the quorum-based (QB) protocols. We show that the processing overhead of each replica can be reduced in the EMQB protocol compared with the QB and MQB protocols.

Design and Evaluation of Multimedia Quorum-Based Synchronization Protocols

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 up-to-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. Each parameter of a replica is read while there is a 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. 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 operation, every replica in the 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.

Multimedia Quorum-based Synchronization Protocols

Replicas of multimedia objects are distributed to peers in overlay networks. Multimedia objects are characterized in terms of not only data structure parameter but also quality of service (QoS) parameters like frame rate. Replicas have to be synchronized to be mutually consistent. Each parameter of a replica is read and written by transactions. Thus, the data structure and QoS parameters of a replica are manipulated. There are enriching and impoverishing types of write operations. Some data is added to a replica in an enriching operation and is removed in an impoverishing operation. In the MQB protocol, the physical state of each replica is not always 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 write operation is issued, every replica is not updated in the quorum. In order to reduce the processing overhead of each replica, we discuss an extended MQB (EMQB) protocol where every replica is not updated even in an enriching write operation. The EMQB 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.