Caching is a proven means to improve scalability and availability of software systems as well as to reduce latency of user requests. In contrast to Web caching where single Web objects are kept ready somewhere in caches in the userto-server path, database caching uses a full-fledged DBMS as a cache to adaptively maintain sets of records from a remote DB and to evaluate queries on them. We give an introduction to the new class of constraint-based DB caching, by the example of cache groups. These cache groups are constructed from parameterized cache constraints, and their use is based on the key concepts of value and domain completeness. We show how cache constraints affect the correctness of query evaluations in the cache and which optimizations they allow. Finally, once unsafe cache configurations, whose performance is uncontrollable, are identified, the costs of safe ones can be analyzed quantitatively
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