The effect of database filters on the performance of buffered relational database systems

摘要

To reduce the load of CPU's, database filters are installed on many database machines to filter out irrelevant data from the mass storage devices. Furthermore, as CPU's are usually much faster than I/O devices, database buffers are also installed on many database systems to avoid additional physical I/O operations. However, after the data pages have been filtered by the database filter, the buffer hit rate may decrease and the performance of the database system degrades accordingly. In this paper, a queueing model is proposed to study the effectiveness of the database filter. The result shows that the system performance can be improved slightly by the database filter. A simulation model is proposed afterwards to compare the performance of database systems with and without the database filter under the execution of various Selection operations. The result concludes that the database filter can only improve the system performance by a factor of 1.24 at most, and the system performance actually degrades in most cases. Based on the performance analysis, the use of the database filter in the buffered database systems is not recommended.