Executing join queries in an uncertain distributed environment

• Authors: D. J. Reid
• Venue: Mathematical and Computer Modelling: An International Journal
• Year: 1995

The uncertainty inherent in the distributed environment poses new challenges to the efficient utilization of system resources in managing database transactions. In response to this realization, the execution of a join query in a system with probabilistic resource and cost parameters is contemplated, leading to the development of stochastic programming models. Information in the form of relational tables and scattered amongst the sites of a distributed database system is to be collated and presented to the appropriate user, in response to an issued request. Performing this task demands the usage of limited resources; the ultimate goal is the determination of an execution strategy incurring minimal cost to the system. The actual state of any network component at the moment of its exploitation cannot be exactly ascertained in advance. Any interrogation of a distant element must be communicated by the network, and this involves a delay, as perceived by the questioner, during which the state of the system may change. Indeed, the time at which a task assigned to any particular component cannot itself be precisely predicted, even if the future state of the component could be known definitively. By considering the uncertain nature of the distributed environment, the earlier model of join query evaluation presented in [1] can be modified in different ways to account for system parameters known only in a stochastic sense. This new level of subjectivity is a revelation of the many different attitudes that may be taken towards the chance of infeasibility in the solution, for the major issue in dealing with uncertainty is the choice of an appropriate measure of risk.