Computer Sciences Dept.

DIRECT: A Multiprocessor Organization for Supporting Relational Database Management Systems

David DeWitt

The design of DIRECT, a multiprocessor organization for supporting relational database management systems is presented. DIRECT has a MIMD (multiple instruction stream, multiple data stream) architecture. It can simultaneously support both intra-query and inter-query concurrency. The number of processors assigned to a query is dynamically determined by the priority of the query, the type and number of relational algebra operations it contains, and the size of the relations referenced. Since DIRECT is a virtual memory machine, the maximum relation size is not limited to that of the associative memory as in some other database machines. Concurrent updates are controlled through the use of locks on relations which are maintained by a controlling processor. DIRECT is being implemented using LSI-11/03 microprocessors and CCD memories which are searched in an associative manner. A novel cross-point switch is used to connect the LSI-11 processors to the CCD memories. While cross-point switches have proven too expensive for use in general purpose parallel processors, their application in DIRECT demonstrates that these switches can be successfully used in specialized applications.

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