Extendible Chained Bucket Hashing for Main Memory Databases

The objective of this paper is to develop a high performance hash-based access method for main memory database systems. Chained bucket hashing is known to provide the fastest random access to a static file stored in main memory. For a dynamic file, however, chained bucket hashing is inappropriate because its address space cannot be adapted to the file size without total reorganization. Extendible hashing which has been proposed in disk-based environment has the ability to accommodate its address space as the file grows or shrinks. However, extendible hashing is impractical in main memory environment because of its large directory size. In this paper, we introduce a new hash-based access method called extendible chained bucket hashing. The method is a complementary integration of chained bucket hashing and extendible hashing for dynamic files in main memory databases. We carried out an experiment to compare our hashing scheme with two existing proposals: linear hashing modified for main memory environment and controlled search multidirectory hashing. The experiment shows that extendible chained bucket hashing outperforms other proposals in both key loading time and search time.