Performance of linear hashing schemes for primary key retrieval

address space allocated to the file to be increased and reduced without reorganizing the whole file. In this paper, we propose a new scheme for dynamic hashing in which the growth of a file occurs at a rate of s per a full expansion, where s and t are given integers and s is smaller than two, as compared to a rate of two in linear hashing. (Note that s is used to denote the number of pages of a file before any split occurs in a full expansion, and t is used to denote the number of pages of the file after a full expansion is finished through a number of split operations.) Therefore, extended spiral hashing can maintain more stable performance through file expansions and has much better storage utilization than does linear hashing. Basically, the proposed scheme is based on a modified spiral storage approach, in which the load distribution is uniform after a full expansion. Therefore, extended spiral hashing can also provide better performance than can the original spiral storage approach. Moreover, we have used a modified separator strategy for overflow handling such that retrieval of any data record in extended spiral hashing is upper-bounded by two disk accesses. From our performance analysis and simulation, extended spiral hashing can achieve nearly 96% storage utilization as compared to 78% storage utilization using linear hashing and 88% storage utilization using the spiral storage approach.

Extended Spiral Hashing for Expansible Files.

Linear hashing is a technique for constructing dynamic files for direct access. It has an advantage over other dynamic methods in that it lacks a directory. However, a weakness of the method is that at high packing factors, it requires more probes on the average to access a record than do many of the static methods. This paper presents a straightforward modification of linear hashing which, according to experimental results, significantly reduces the average number of retrieval probes in almost aft cases when compared with standard linear hashing. The parameter of overflow page size is an important one for adjusting performance. By choosing an appropriate overflow page size, the user may obtain results which are also better or comparable to those of other variants of linear hashing. In addition, the paper analyzes the effects of varying the primary page size, the overflow page size, and the packing factor on retrieval performance.

Willard D. Ruchte

Papers

Linear hashing with Priority Splitting: A method for improving the retrieval performance of linear hashing