Dynamic Load Balancing in Parallel Database Systems

Parallel database systems have to support both inter-transaction as well as intra-transaction parallelism. Inter-transaction parallelism (multi-user mode) is required to achieve high throughput, in particular for OLTP transactions, and sufficient cost-effectiveness. Intratransaction parallelism is a prerequisite for reducing the response time of complex and dataintensive transactions (queries). In order to achieve both goals dynamic strategies for load balancing and scheduling are necessary which take the current system state into account for allocating transactions and subqueries to processors and for determining the degree of intraquery parallelism. We study these issues for the major approaches of parallel database systems, Shared Nothing and Shared Disk, and for parallel scan and join processing in multi-