Heuristic Reorganization of Clustered Files

The problem of file reorganization which we consider involves altering the placement of records on pages of a secondary storage device. In addition, we want this reorganization to be done in-place, i.e., using the file's original storage space for the newly reorganized file. The motivation for such a physical change is to improve the database system's performance. For example, by placing frequently and jointly accessed records on the same page or pages, we can try to minimize the number of page accesses made in answering a set of queries. The optimal assignment (or reassignment) of records to clusters is exactly what record clustering algorithms [1,2,4,9] attempt to do. However, record clustering algorithms usually do not solve the entire problem, i.e., they do not specify how to efficiently reorganize the file to reflect the clustering assignment which they determine. Our algorithm is a companion to general record clustering algorithms since it actually transforms the file. The problem of optimal file reorganization is NP-hard [3]. Consequently, our reorganization algorithm is based on heuristics for which we prove three important observations.