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A number of algorithms have been proposed for accessing B-trees concurrently, but the performance of these algorithmsis not yet well understood.In this paper, we study the performance of various concurrency control algorithms using a detailed simulation model of B-tree operations in a centralized DBMS. Our study considers a wide range of data contention situations and resource conditions.Results from our experiments indicate that algorithms in which updaters lock-couple using exclusive locks perform poorly as compared to those that permit more optimistic index descents.In particular, the B-link algorithms provide the most concurrency and the best overall performance.

A number of algorithms have been proposed to access B+-trees concurrently, but they are not well understood. In this article, we study the performance of various B +-tree concurrency control algorithms using a detailed simulation model of B+-tree operations in a centralized DBMS. Our study covers a wide range of data contention situations and resource conditions. In addition, based on the performance of the set of B +-tree concurrency control algorithms, which includes one new algorithm, we make projections regarding the performance of other algorithms in the literature. Our results indicate that algorithms with updaters that lock-couple using exclusive locks perform poorly as compared to those that permit more optimistic index descents. In particular, the B-link algorithms are seen to provide the most concurrency and the best overall performance. Finally, we demonstrate the need for a highly concurrent long-term lock holding strategy to obtain the full benefits of a highly concurrent algorithm for index operations.

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