Performance evaluation of processor allocation algorithms for parallel query execution

Two processor allocation algorithms are presented based on a query cost model incorporating the effects of data cormnunication overheads and load imbalance running on a shared nothing parallel architecture. The phase-based algorithm makes use of the heuristic of merge-point evaluation so that the number of operations in each execution phase are distributed evenly. Time equalisation technique is employed within each phase to minimise phase execution time. The non phase-based algorithm is a dynamic approach and its performance is sensitive to the number of processors available. Basea on the algorithm, the operations in the query tree are c :ecuted in such a order that leaf operations are conducted first and processing is ended with the root operation. The concept of optimal degree of parallelism for each operation is also introduced and the new algorithms are evaluated with a simulation study. The experimental results show that the new algorithms outperform the conventional processor allocation algorithms. In addition, the phase based algorithm always provides a local phase optimisation and the non phase based algorithm gives a global optimal solution when there is a large number of processors available.