A cautious scheduler for multistep transactions
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Given a classC of serializable schedules, a cautiousC-scheduler is an on-line transaction scheduler that outputs schedules in classC and never resorts to rollbacks. Such a scheduler grants the current request if and only if the partial schedule it has granted so far, followed by the current request, can be extended to a schedule inC. A suitable extension is searched among the set of all possible sequences of the pending steps, which are predeclared by the transactions whose first requests have already arrived. If the partial schedule cannot be extended to a schedule inC, then the current request is delayed. An efficient cautiousCPSR-scheduler has been proposed by Casanova and Bernstein.
This paper discusses cautiousWRW-scheduling, whereWRW is the largest polynomially recognizable subclass of serializable schedules currently known. Since cautiousWRW-scheduling is, in general, NP-complete as shown in this paper, we introduce, a subclass (namedWRW #) ofWRW and discuss an efficient cautiousWRW #-scheduler. We also show that the fixed point set of the cautiousWRW #-scheduler properly containsCPSR. Therefore, ourWRW #-scheduler allows more concurrency than anyCPSR- scheduler.
Key wordsDatabase systems Concurrency control Serialized ability Transaction scheduler
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- G. N. Buckley and A. Silberschatz, Obtaining progressive protocols for a simple multiversion database model,Proc. 9th Int. Conf. on VLDB, Oct/Nov 1983, pp. 74–80.Google Scholar
- M. J. Carey, The performance of concurrency control algorithms for database management systems, Computer Sciences Tech. Rept. No. 530, University of Wisconsin, Madison, 1984.Google Scholar
- M. A. Casanova, The concurrency control problem for database systems, Lecture Notes in Computer Science, Vol. 116, Springer-Verlag, Berlin, 1981.Google Scholar
- T. Ibaraki, T. Kameda, and T. Minoura, Serializability made simple, Tech. Rept. LCCRTR82-12, Department of CS, Simon Fraser University, Burnaby, BC, Dec. 1982.Google Scholar
- T. Ibaraki, T. Kameda, and T. Minoura, Disjoint-interval topological sort: a useful concept in serializability theory,Proc. 9th Int. Conf. on VLDB, Oct/Nov 1983, pp. 89–91.Google Scholar
- T. Ibaraki, T. Kameda, and N. Katoh, Cautious transaction schedulers for database concurrency control, LCCR Tech. Rep. 85-6, Laboratory for Computer and Communications Research, Simon Fraser University, Burnaby, BC, 1985.Google Scholar
- H. T. Kung and C. H. Papadimitriou, An optimality theory of concurrency control for databases,Proc. ACM-SIGMOD Int. Conf. on Management of Data, Boston, May 1979, pp. 116–126.Google Scholar
- R. Sethi, A model of concurrent database transactions,Proc. 22nd IEEE Symp. Foundation of Comp. Sci., Oct. 1981, pp. 175–184.Google Scholar
- M. Yannakakis, Issues of correctness in database concurrency control by locking,Proc. ACM Symp. Theory of Computing, May 1981, pp. 363–367.Google Scholar