A Self-Adaptive Database Buffer Replacement Scheme.

The overall performance of a database system is very sensitive to the buffer replacement algorithm used. However, the performance evaluation of database buffer replacement algorithms commonly assumes that database accesses are independent and the probability for each individual database record to be accessed is fixed. Due to these rigid assumptions, the results of performance evaluation are not always reliable. In this dissertation, we apply Simon\u27s model of information accessing to model database accessing frequencies. This approach relaxes the independent assumption, and since it also allows certain dynamic behavior in accessing frequencies; thus, it is more robust and preferable over the traditional artificial data approach. Furthermore, taking advantage of the conceptual similarity between the self-organizing linear search heuristics and the traditional buffer replacement algorithms, we propose a self-adaptive buffer replacement scheme that outperforms conventional database buffer replacement algorithms. The findings of our study can be further applied to many other computer applications, e.g. the more complex problem of archival storage design in larger database systems

Efficient caching algorithms for memory management in computer systems

As disk performance continues to lag behind that of memory systems and processors, fully utilizing memory to reduce disk accesses is a highly effective effort to improve the entire system performance. Furthermore, to serve the applications running on a computer in distributed systems, not only the local memory but also the memory on remote servers must be effectively managed to minimize I/O operations. The critical challenges in an effective memory cache management include: (1) Insightfully understanding and quantifying the locality inherent in the memory access requests; (2) Effectively utilizing the locality information in replacement algorithms; (3) Intelligently placing and replacing data in the multi-level caches of a distributed system; (4) Ensuring that the overheads of the proposed schemes are acceptable.;This dissertation provides solutions and makes unique and novel contributions in application locality quantification, general replacement algorithms, low-cost replacement policy, thrashing protection, as well as multi-level cache management in a distributed system. First, the dissertation proposes a new method to quantify locality strength, and accurately to identify the data with strong locality. It also provides a new replacement algorithm, which significantly outperforms existing algorithms. Second, considering the extremely low-cost requirements on replacement policies in virtual memory management, the dissertation proposes a policy meeting the requirements, and considerably exceeding the performance existing policies. Third, the dissertation provides an effective scheme to protect the system from thrashing for running memory-intensive applications. Finally, the dissertation provides a multi-level block placement and replacement protocol in a distributed client-server environment, exploiting non-uniform locality strengths in the I/O access requests.;The methodology used in this study include careful application behavior characterization, system requirement analysis, algorithm designs, trace-driven simulation, and system implementations. A main conclusion of the work is that there is still much room for innovation and significant performance improvement for the seemingly mature and stable policies that have been broadly used in the current operating system design