Strategies for enhancing concurrency and managing deadlocks in data base locking protocols
C. Mohan · 1981
With the ever growing popularity of data base management the systematic study of consistency preserving concurrency control techniques has become very important. Two important issues that need to be considered are: (i) the level of concurrency and (ii) deadlocks. This thesis is concerned with the problem of extending previous work on two-phase and non-two-phase locking protocols to achieve a higher degree of concurrency and at the same time deal effectively with the deadlock problem. Our work with the non-two-phase protocols deals with the most general of the existing natural protocols that are defined for use with data bases organized as directed acyclic graphs. An increased level of concurrency is attained by allowing lock conversions and/or by introducing new lock modes. When this is done either deadlock-freedom is assured a priori or simple restrictions are introduced to reduce the cost of deadlock detection and recovery. In addition to extending existing proctocols and proposing new ones, we also extend the existing theory of locking protocols by including lock conversions and the new modes of locking in the directed hypergraph model of locking protocols. In so doing, we obtain very general results concerning serializability and deadlock-freedom properties of all protocols satisfying a natural closure property. We propose and use some new proof techniques.