Middleware Object query Processing with Deferred Updates and Autonomous Sources

摘要

This paper presents a query processing algorithm called DECAF for use in middleware object query systems that are based on the use of an object cache. The DECAF algorithm is designed to work correctly even in the presence of updates to the underlying databases that don't go through the object cache (i.e., even for autonomous data sources that can be updated through legacy applications that do not perform their updates thorugh the middleware object layer). DECAF's query resutls are consistent with updates performed by such transactions; its results are also consistent with any deferred updates that are present in the ojbect cache but not yet committed at the database server. The DECAF algorithm attempts to push down query predicates to the underlying DBMSs to take advatnage of the query processing capabilities of these systems and to reduce the amount of data transferred from these systems to the object cache.