Abstract

With relations growing larger and queries becoming more complex, parallel query processing is an increasingly attractive option for improving the performance of database systems. The objective of this paper is to examine the various issues encountered in parallel query processing and the techniques available for addressing these issues. The focus of the paper is on the join operation with both sort-merge join and hash joins being considered. Three types of parallelism can be exploited, namely intra-operator, inter-operator, and inter-query parallelism. In intra-operator parallelism the major issue is task creation, and the objective is to split a join operation into tasks in a manner such that the load can be spread evenly across a given number of processors. This is a challenge when the values on the join attribute are not uniformly distributed. Inter-operator parallelism can be achieved either through parallel execution of independent operations or through pipelining. In either case,...

Citations