Very few analytic models have been reported for distributed database systems, perhaps because of complex relationships of the different kinds of resources in them. Layered queueing models seem to be a natural framework for these systems, capable of modelling all the different features which are important for performance (e.g. devices, communications, multithreaded processes, locking). To demonstrate the suitability of the layered framework, a previous queueing study of the CARAT distributed testbed has been recast as a layered model. Whereas the queueing model bears no obvious resemblance to the database system, the layered model directly reflects its architecture. The layered model predictions have about the same accuracy as the queueing model.
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