The bounded disorder access method

A new key associative access method, called the bounded disorder method, is described. The method uses a combination of hashing and tree indexing. The method has very good random access performance, being comparable to the best hashing methods if its small index is stored entirely in main memory. The method's advantage compared with hashing is that range searches are possible while searching only a portion of the file proportional to the size of the range. It is possible to control index size by controlling node size. Node size can be increased without increasing the amount of data transferred during a random probe. Further, increasing node size has only a minor effect on key sequential access performance. Even quite large nodes, so long as they can be read into memory in their entirety, have good key sequential performance. The bounded disorder method is the only one of the methods employing large nodes that can cope well with arbitrary key distributions. These properties make the bounded disorder method a good choice as the only access method of a data base system.