On a more realistic lock contention model and its analysis

Abstract

Most performance modeling studies of lock contention in transaction processing systems are deficient in that they postulate a homogeneous database access model. The non-homogeneous database access model described in this paper allows multiple transaction classes with different access patterns to the database regions. The performance of the system from the viewpoint of lock contention is analyzed in the context of the standard two-phase locking concurrency control method with the general waiting policy. The approximate analysis is based on mean values of parameters and derives expressions for the probability of lock conflict (usually leading to transaction blocking) and the mean blocking time. The latter requires estimating the distribution of the effective wait-depth encountered by blocked transactions and the mean waiting time associated with different blocking levels. The accuracy of the analysis is validated against simulation results and also shown to be more accurate than analytic solutions considering only two levels of transaction blocking. Previously proposed metrics for load control have limited applicability for the model under consideration.