Determining the Number of Remote Sites Accessed in Distributed Transaction Processing

We characterize the number of remote accesses and the number of distinct remote sites accessed by global transactions in a distributed database environment. Both measures are important in determining the overhead of distributed transaction processing and are affected by the distribution of transaction size (number of distinct objects accessed by a transaction) and the distribution of remote accesses made by a transaction. Keeping the mean transaction size fixed, we show that in the case of some commonly used distributions for the number of remote accesses (e.g., the binomial and uniform distribution) variable size transactions access a fewer number of distinct remote sites on the average than fixed size transactions. Also for these and some other distributions (for the number of remote accesses) the mean number of remote accesses is independent of the distribution of transaction size, but this is not generally true. In cases when variable size transactions have a higher mean number of remote accesses than fixed size transactions, fixed size transactions still tend to access a larger number of remote sites than variable size transactions, but this is not always true when variable size transactions have a higher mean for the number of remote accesses than fixed size transactions.