Priority Scheduling of Transactions in Distributed Real-TimeDatabases

  • Authors:

  • Victor C. S. Lee;Kam-Yiu Lam;Ben Kao

  • Affiliations:

  • Dept. of Computer Science, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong;Dept. of Computer Science, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong;Dept. of Computer Science, The University of Hong Kong, Pokfulam, Hong Kong

  • Venue:
  • Real-Time Systems
  • Year:
  • 1999

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Abstract

One of the most important issuesin the design of distributed real-time database system (DRTDBS)is transaction scheduling which consists of two parts: priorityscheduling and real-time concurrency control. In the past studies,mostly, these issues are studied separately although they havea very close interaction with each other. In this paper, we proposenew priority assignment policies for DRTDBS and study their impacton two typical real-time concurrency control protocols (RT-CCPs),High Priority Two Phase Locking (HP-2PL) and Optimistic ConcurrencyControl with Broadcast Commit (OCC-BC). Our performance resultsshow that many factors, such as data conflict resolution, degreeof data contention and transaction restarts, that are uniqueto database systems, have significant impact on the performanceof the policies which in turn affect the performance of the real-timeconcurrency control protocols. OCC-BC is more affected by thepriority assignment policies than HP-2PL owing to the late detectionof conflict. In the design of priority assignment policies, wehave found that neither the purely deadline driven policies nordata contention driven policies are suitable for DRTDBS. Ourproposed policy, the Mixed Method (MM), which considers bothtransaction timeliness and data contention, outperforms otherpolicies over a wide range of system parameter settings.