PARTIAL INDEXING FOR NONUNIFORM DATA DISTRIBUTIONS IN RELATIONAL DBMS

It is well known that the effectiveness of relational database systems is greatly dependent on the efficiency of the data access strategies. For this reason, much work has been devoted to the development of new access techniques, supported by adequate access structures such as th e B+trees. The effectiveness of the B+tree also depends on the data di stribution characteristics; in particular, poor performance results wh en the data show strong key value distribution unbalancing. The aim of this paper is to present the partial index: a new access structure th at is useful in such cases of unbalancing, as an alternative to the Btree unclustered indexes. The access structures are built in the physi cal design phase, and at execution (or compilation) time, the optimize r chooses the most efficient access path. Thus, integration of the par tial indexing technique in the design and in the optimization process are also described.