An analytical model for the performance of concurrent B tree algorithms

A dictionary is an abstract data type supporting the actions search, insert, and delete. Search structures are data structure used to implement a dictionary, e.g. B trees, hash structures, grid files, etc. Many concurrent algorithms for search structures have been proposed, but relatively little work has addressed their performance. This paper proposes an analytic performance model for a range of concurrent algorithms on B+ trees. It uses this model to propose a high performance, simple-to-program variant of lockcoupling algorithms. The model actually consists of two mutually exclusive models: a ‘‘constant flow’’ model in which the throughput is assumed to remain at its average value; and a ‘‘bursty flow’’ model in which the throughput is predicted to oscillate with a certain frequency and amplitude based on the number of processes, the height of the tree, and the size of the nodes. We find that the data points from simulation fall between these two predictive models, tending towards the bursty flow one as the number of processors increases. Inasmuch as the analytical model characterizes B+ trees in terms of fanout, height, probability of restructuring, and node size, it does not depend on the details of B+ trees and so can be extended, at least in spirit, to other structures.