INTRODUCTION
The development of database management systems has coincided with significant
developments in distributed computing and processing technologies. The merging ofthese two
resources has resulted in the emergence of parallel database management systems. These
systems have become the dominant data-management tools for highly data-intensive
applications.
A distributed database is a collection of multiple, logically interrelated databases
distributed over a computer network. A distributed database management system is then
defined as the software system that permits the management of the distributed database and
makes the distribution transparent to the users.
A parallel database system can be defined as a database management system
implemented on a tightly coupled multiprocessor. An important distinction between a parallel
DBMS and a distributed DBMS is that distributed DBMSs assume loose interconnection
between processors that have their own operating systems and operate independently. Parallel
DBMSs exploit multi-processor architectures in order to build high-performance and
high-availability database servers.
Inthe followingsections we look at three main issues concerning paralleldatabase systems
performance : architecture, data placement and reallocation, and query optimization. In each
section a brief explanation is provided about the various performance improvement possibilities
and their summary.