1Parallel Query Processing in Shared Disk Database Systems

System developments and research on parallel query processing have concentrated either on "Shared Everything " or "Shared Nothing " architectures so far. While there are several com-mercial DBMS based on the "Shared Disk " alternative, this architecture has received very little attention with respect to parallel query processing. This paper is intended as a first step to close this gap. A detailed comparison between Shared Disk and Shared Nothing reveals many potential benefits for Shared Disk with respect to parallel query processing. In partic-ular, Shared Disk supports more flexible control over the communication overhead for intra-transaction parallelism, and a higher potential for dynamic load balancing and efficient pro-cessing of mixed OLTP / query workloads. We also outline necessary extensions for trans-action management (concurrency/coherency control, logging/recovery) to support intra-transaction parallelism in the Shared Disk environment.