ANALYSIS OF IMPACT OF NETWORK DELAY ON MULTIVERSION CONSERVATIVE TIMESTAMP ALGORITHMS IN DDBS

In a distributed environment, users access databases in remote sites v ia a communication network. The randomness of the network delay may ca use operations to arrive at the remote sites out of sequence. Multiver sion conservative timestamp algorithms can be used to schedule the ope rations to maintain the consistency of the databases. We model the alg orithms as queueing systems with partial order resequencing constraint s, where the resequencing constraints vary as the number of versions i n the algorithms. Under the assumption of an lid network delay, the di stributions of the response time of operations and the buffer occupanc y in the resequencing buffer are derived analytically for the algorith ms with version number one to infinity. The impact of the network dela y on the performance of the DDBS is investigated. It is found that the variance of the network delay has significant effect on the system pe rformance.