Oracle Corporation
Systems and methods for compressing keys in hierarchical data structures

Abstract:

The present disclosure describes systems and methods for enhancing the space utilization of storing keys in hierarchical data structures, such as B+Tree leaf blocks, by partially or fully compressing the keys. Partially compressing the keys may include storing certain keys as offsets from a start key. Fully compressing the keys may include setting a "type" value included in the header of the leaf block to a value indicating that the keys are implicitly represented by an ordinal key index, which defines the ordinal arrangement of keys in the leaf block. Partially or fully compressing keys, according to the implementations described herein, reduces the amount of space needed to store keys in a leaf block of a B+Tree.