In a distributed environment, users access databases in remote sites via a communication network. The randomness of the network delay may cause operations to arrive at the remote sites out of sequence. Multiversion conservative timestamp algorithms can be used to schedule the operations to maintain the consistency of the databases. We model the algorithms as queueing systems with partial order resequencing constraints, where the resequencing constraints vary as the number of versions in the algorithms. Under the assumption of an iid network delay, the distributions of the response time of operations and the buffer occupancy in the resequencing buffer are derived analytically for the algorithms with version number one to infinity. The impact of the network delay on the performance of the DDBS is investigated. It is found that the variance of the network delay has significant effect on the system performance.
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