Unifying Concurrency Control and Recovery of Transactions with Semantically Rich Operations

The classical theory of transaction management contains two different aspects, namely concurrency control and recovery, which ensure serializability and atomicity of transaction executions, respectively. Although concurrency control and recovery are not independent of each other, the criteria for these two aspects were developed orthogonally and as a result, in most cases these criteria are incompatible with each other. Recently a unified theory of concurrency control and recovery for databases with read and write operations has been introduced in [19, l] that allows reasoning about serializability and atomic@ within the same framework. In [19, 11 a class of schedules (called prejix reducible), which guarantees both serializability and atomicity in a failure prone environment with read/write operations was introduced. Several protocols were developed to generate such schedules by a database concurrency control mechanism. We present here a unified transaction model for databases with an arbitrary set of semantically rich operations. We investigate constructive characterization of the class of prefix reducible schedules with semantically rich operations. It turns out that unlike databases with only read/write operations, the exact characterization of prefix reducible schedules in databases with arbitrary operations is rather infeasible. Thus, we propose here several sufficiently rich subclasses of prefix reducible schedules, and design concurrency control protocols that guarantee both serializability and atomic&-y for schedules from these classes.