Description

Parallel database systems have to support the effective parallelization of complex queries in multi-user mode, i.e. in combination with inter-query/inter-transaction parallelism. For this purpose, dynamic scheduling and load balancing strategies are necessary that consider the current system state for determining the degree of intra-query parallelism and for selecting the processors for executing subqueries. We study these issues for parallel hash join processing and show that the two subproblems should be addressed in an integrated way. Even more importantly, however, is the use of a multiresource load balancing approach that considers all potential bottleneck resources, in particular memory, disk and CPU. We discuss basic performance tradeoffs to consider and evaluate the performance of several load balancing strategies by means of a detailed simulation model. Simulation results will be analyzed for multi-user configurations with both homogeneous and heterogeneous (query/OLTP) workloads.