Flexible Cache for Database Management Systems

Cache of a persistent data structure represents an important part, which significantly influence its efficiency. Cache consists from an array of main memory blocks (caled cache nodes) with a constant size. Cache nodes buffer the data structure nodes hence they can be accessed quickly. However, data structure nodes do not usually fully utilize the whole main memory block. Therefore, the constant cache node size the waste of the main memory. In this article, we propose the solution where the cache consists from the cache nodes with a different size. Cache is split into several cache rows. The data structure nodes with the similar size are stored in one cache row. Such a solution has two problems: (1) that the some cache row has to replace the nodes too often during the querying (cache row contention), and (2) that the data structure nodes has to be moved between the cache rows during the insert and the delete operation. In our experimental section we show that the effect of the cache row contention is minimized if we set the cache row size according to the data structure node distribution. We also discuss a solution of the node cache moves problem.