Tolerating bounded inconsistency for increasing concurrency in database systems

Abstract

Recently, the scope of databases has been extended to many non-standard applications, and serializability is found to be too restrictive for such applications. In general, two approaches are adopted to address this problem. The first approach considers placing more structure on data objects to exploit type specific properties while keeping serializability as the correctness criterion. The other approach uses explicit semantics of transactions and databases to permit interleaved executions of transactions that are non-serializable. In this paper, we attempt to bridge the gap between the two approaches by using the notion of serializability with bounded inconsistency. Users are free to specifiy the maximum level of inconsistency that can be allowed in the executions of operations dynamically. In particular, if no inconsistency is allowed in the execution of any operation, the protocol will be reduced to a standard strict two phase locking protocol based on type-specific semantics of data objects. Bounded inconsistency can be applied to many areas which do not require exact values of the data such as for gathering information for statistical purpose, for making high level decisions and reasoning in expert systems which can tolerate uncertainty in input data.