A mean value performance model for locking in databases

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Abstract
A new performance model for dynamic locking is proposed. It is based on a flow diagram and uses only the steady state average values of the variables. It is general enough to handle nonuniform access, shared locks, static locking, multiple transaction classes, and transactions of indeterminate length. The analysis is restricted to the case in which all conflicts are resolved by restarts. It has been shown elsewhere that, under certain conditions, this pure restart policy is as good as, if not better than, a policy that uses both blocking and restarts. The analysis is straightforward, and the computational complexity of the solution, given some nonrestrictive approximations, does not depend on the input parameters. The solution is also well defined and well behaved. The model's predictions agree well with simulation results. The model shows that data contention can cause the throughput to thrash, and gives a limit on the workload that will prevent this. It also shows that systems with a particular kind of nonuniform access and systems in which transactions share locks are equivalent to systems in which there is uniform access and only exclusive locking. Static locking has higher throughput, but longer response time, than dynamic locking. Replacing updates by queries in a multiprogramming mix may degrade performance if the queries are longer than the updates.