Distributed data management in a real-time environment

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Distributed data management in a real-time environment

Moore, R.B.

This paper considers the problems of distributed data processing in a naval command and control environment. The constraints of real-time responses and resilience to damage pose problems quite distinct from those of the commercial environment (where database systems are usually found). Research has been carried out for the Admiralty Research Establishment (ARE) by Software Sciences Ltd in an attempt to adopt a database approach not only to the basic problems of data management but also to the problems of coordinating a geographically distributed command and control system. The main product of this research has been a working prototype of a real time distributed database manager: ADDAM (the ARE Distributed DAtabase Manager) which maintains the database in a partitioned replicated fashion, and dynamically allocates data to those nodes with a need for it. The methods ADDAM uses to solve the problems of distributed database management, within the constraints of the naval requirements, are described. Particular attention is paid to the problem of altering the database at real time rates without either compromising the integrity of the data, or reducing the availability of the data by locking records for prolonged periods of time. ADDAM utilises two protocols; one which uses minimal consistency checking to provide very rapid updates, and a second protocol which uses a three phase commit protocol to ensure that updates are faithfully represented on all copies of the database.