Replica Control Protocol Research Articles

Formal Development of Fault-Tolerant Majority Based Replica Control Protocol using Event-B

In distributed environment, data availability and concurrency control both are challenging issues. Data availability can be maintained by replicating data at several locations or sites that will improve the availability but at the same time it is very challenging task to maintain the consistency of it. In order to improve the performance of the system, it is required to execute multiple transactions concurrently on several sites. Therefore, we need to control these concurrent transactions for maintaining consistency of replica. Replica control become more complex for the environment where messages are delayed due to communication failure. In this paper, we develop formal model of fault-tolerant replica control protocol Using Event-B. Formal methods are mathematical techniques through which we can verify the correctness of model. Event-B is a formal method which is used to develop the model in distributed environment.

A HIGH AVAILABILITY CLUSTER-BASED REPLICA CONTROL PROTOCOL IN DATA GRID

Data replication is widely used to provide high data availability, and increase the performance of the distributed systems. Many replica control protocols have been proposed in distributed and grid environments that achieved both high performance and availability. However, the previously proposed protocols still require a bigger number of replicas for read and write operations which are not suitable for a large scale system such as data grid. In this paper, a new replica control protocol called Clusteringbased Hybrid (CBH) has been proposed for managing the data in grid environments. We analyzed the communication cost and data availability for the operations and compared CBH protocol with recently proposed replica control protocols called Dynamic Hybrid (DH) protocol and Diagonal Replication in 2D Mesh (DR2M) protocol. To evaluate CBH protocol, a simulation model was implemented using Java. Our results show that for the read operations, CBH protocol improves the performance of communication cost and data availability compared to the DH and DR2M protocols.

A CLUSTERING-BASED HYBRID REPLICA CONTROL PROTOCOL FOR HIGH AVAILABILITY IN GRID ENVIRONMENT

In recent years, with the emergence of grid computing system, the number of distributed sites has become very large. When thousands of sites involved in a grid computing system, data replication can improve data availability, communication cost and provide fault-tolerance in the system. In the literature, many replica control protocols have been proposed for managing replicated data. However, in large scale distributed system, most of these protocols still require a bigger number of replicas for maintaining consistency, thus degrade the performance of the protocols. Therefore, in this study, we proposed a new replica control protocol named Clustering-Based Hybrid (CBH) protocol. CBH protocol employs a hybrid replication strategy by combining the advantages of two common replica control protocols into one to improve the performance of the existing protocols. We analyzed the communication cost and availability of the operations and compare CBH protocol with recently proposed replica control protocol named Dynamic Hybrid (DH) protocol. A simulation model was developed using Java to evaluate CBH protocol. Our results show that the proposed protocol provides lower communication cost and higher data availability than DH protocol.

High Availability with Diagonal Replication in 2D Mesh (DR2M) Protocol for Grid Environment

Replication is a useful technique for distributed database systems and has been implemented in EU data grid and HEP in CERN for handling huge data access. Replica selection in their prototypes still can be enhanced to provide high availability, fault tolerant and low in communication cost. This paper introduces a new replica control protocol, named Diagonal Replication in 2D Mesh (DR2M) for grid environment and compares its performance with the previous protocols. The performance in this paper is data availability for read and write operation, which are compared to the Read-One Write-All (ROWA), Voting (VT), Tree Quorum (TQ), Grid Configuration (GC), Three Dimensional Grid Structure (TDGS), and Diagonal Replication on Grid (DRG). This paper discusses the protocol of replicating data for grid environment, putting the protocol in a logical 2D mesh structure by employing the quorums and voting techniques. The data file is copied in a selected replica from the diagonal sites in each quorum. The selection of a replica depends on the diagonal location of the structured 2D mesh network where the middle replica is selected because it is the shortest path to get a copy of the data from most of the direction in the quorum. The algorithm in this paper also calculates the optimized number of nodes to be grouped in each quorum and how many quorums are needed for the number of nodes, N in a network. DR2M protocol also ensures that the data for read and write operations are consistent, by ensuring the quorum must not have a nonempty intersection quorum. To evaluate the DR2M protocol, we developed a simulation model in Java. Our results prove that our protocol improves the performance of data availability compared to the previous data replication protocol, namely Read-One Write-All (ROWA), Voting (VT), Tree Quorum (TQ), Grid Configuration (GC), Three Dimensional Grid Structure (TDGS), and Diagonal Replication on Grid (DRG).

Improving the flexibility for replicated data management in distributed database systems

This paper presents a novel scheme for implementing the flexible replica control protocol[13] in the distributed database systems. The scheme requires less nodes to be locked to perform the read(write) operations. This not only provides better performance, but also provides the system designer extra flexibility to implement the protocol.

The column protocol: A high availability and low message cost solution for managing replicated data

This paper presents a quorum-based replica control protocol which is resilient to network partitioning. In the best case, the protocol generates quorums of a constant size. When some replicas are inaccessible, the quorum size increases gradually and may be as large as O( n), where n is the number of replicas. However, the expected quorum size is shown to remain constant as n grows. This is a desirable property since the message cost for accessing replicated data is directly proportional to the quorum size. Moreover, the availability of the protocol is shown to be comparably high. With the two properties—constant expected quorum size and comparably high availability—the protocol is thus practical for managing replicated data.

Coterie join algorithm

Given a set of nodes in a distributed system, a coterie is a collection of subsets of the set of nodes such that any two subsets have a nonempty intersection and are not properly contained in one another. A subset of nodes in a coterie is called a quorum. An algorithm, called the join algorithm, which takes nonempty coteries as input, and returns a new, larger coterie called a composite coterie is introduced. It is proved that a composite coterie is nondominated if and only if the input coteries are nondominated. Using the algorithm, dominated or nondominated coteries may be easily constructed for a large number of nodes. An efficient method for determining whether a given set of nodes contains a quorum of a composite coterie is presented. As an example, tree coteries are generalized using the join algorithm, and it is proved that tree coteries are nondominated. It is shown that the join algorithm may be used to generate read and write quorums which may be used by a replica control protocol. >

Maintaining availability in partitioned replicated databases

In a replicated database, a data item may have copies residing on several sites. A replica control protocol is necessary to ensure that data items with several copies behave as if they consist of a single copy, as far as users can tell. We describe a new replica control protocol that allows the accessing of data in spite of site failures and network partitioning. This protocol provides the database designer with a large degree of flexibility in deciding the degree of data availability, as well as the cost of accessing data.

Concurrency versus availability: atomicity mechanisms for replicated data

A replicated object is a typed data object that is stored redundantly at multiple locations to enhance availability. Most techniques for managing replicated data have a two-level structure: At the higher level, a replica-control protocol reconstructs the object's state from its distributed components, and at the lower level, a standard concurrency-control protocol synchronizes accesses to the individual components. This paper explores an alternative approach to managing replicated data by presenting two replication methods in which concurrency control and replica management are handled by a single integrated protocol. These integrated protocols permit more concurrency than independent protocols, and they allow availability and concurrency to be traded off: Constraints on concurrency may be relaxed if constraints on availability are tightened, and vice versa. In general, constraints on concurrency and availability cannot be minimized simultaneously.