A Cooperative Caching Architecture for Improving Database Queries: Doctoral Thesis

Client side caching is a commonly used technique for reducing the response time of database queries. Semantic caching is a database caching approach in which results of old queries are cached and used for answering new queries. A new query will be split in a part that retrieves the portion of the result, which is available in a local cache (probe query) and a query that retrieves missing n-tuples for the database server (remainder query). This approach is especially suited for low-bandwidth environments or when database server is under heavy load. Semantic caching was successfully applied for optimizing the execution of queries on mobile clients or over lousy-coupled wide-area networks. Peer-to-Peer(P2P) networks have been applied successfully for improving the performance of cache systems. This thesis aims to use a P2P approach in order to enhance the semantic caching technique.Therefore, The Cooperative Semantic Caching (CoopSC) approach extends the general semantic caching mechanism by using a P2P (Peer-to-peer) approach in order to enable clients to share their local semantic caches in a cooperative manner. When executing a query, the content of both the local semantic cache and entries stored in caches of other clients can be used. A new query will be split into a probe, remote probes, and a remainder query. The probe retrieves the part of the answer which is available in the local cache. Remote probes retrieve those parts of the query which are available in caches of other clients. The remainder retrieves the missing n-tuples from the server. In order to execute the query rewriting, the cache entries of all clients are indexed in a distributed data structure built on top of a P2P overlay that is formed by all clients which are interrogating a particular database server. The general cooperative semantic approach also contains a mechanism for handling operations that modify the content of the database. During this thesis, the general approach was applied in the context of two real-life use-cases: cloud-computing environments, and NetFlow-based network monitoring solutions.This thesis shows that a cooperative semantic caching approach is technical feasible and such an approach approach increases the performance of databases systems. Moreover, in the context of such an approach, update handling can be executed with a reasonable performance when read-intensive workloads are executed. Finally the general CoopSC approach presents economic advantages when used within cloud-computing environments and improves the performance of NefFlow-based network monitoring solutions.