An extension of access paths to improve joins and selections

Abstract

A new access method, based upon predicate-tree and previously presented in [GARD 83b, VALD 84, GARD 85], presents major possibilities of applications. The basic method which is implemented, allows the clustering of tuples from a relation when they satisfy some predicate. The aim of this paper, is to show the flexibility of this method and the numerous possibilities of extensions. In addition, to the permanent access paths based upon physical clustering, predicate-trees allow the implementation of classical secondary access paths. We give a method to code the values of several secondary attributes by use of secondary predicate-trees. This method requires a less important storage volume than classical secondary indexes. Predicate-trees can also efficiently speed up the join operation. Clustering information is used to limit the join to relevant pairs of partitions. Our evaluation shows that an improvement ratio of 7 or more versus traditional algorithms can be achieved.