The Grid File

TLDR

Traditional file structures designed for single-key access, such as inverted files, have deficiencies when used for multikey access to highly dynamic files. The study investigates dynamic, key-symmetric file structures that avoid primary/secondary key distinctions, aiming to design the grid file. Using a bitmap-based compression of a large sparse matrix, the authors introduce a grid partition and grid directory that form the basis of the dynamic grid file. The grid file adapts gracefully to insertions and deletions, achieving at most two disk accesses for single-record retrieval while efficiently supporting range and partially specified queries.

Abstract

Traditional file structures that provide multikey access to records, for example, inverted files, are extensions of file structures originally designed for single-key access. They manifest various deficiencies in particular for multikey access to highly dynamic files. We study the dynamic aspects of file structures that treat all keys symmetrically, that is, file structures which avoid the distinction between primary and secondary keys. We start from a bitmap approach and treat the problem of file design as one of data compression of a large sparse matrix. This leads to the notions of a grid partition of the search space and of a grid directory , which are the keys to a dynamic file structure called the grid file . This file system adapts gracefully to its contents under insertions and deletions, and thus achieves an upper bound of two disk accesses for single record retrieval; it also handles range queries and partially specified queries efficiently. We discuss in detail the design decisions that led to the grid file, present simulation results of its behavior, and compare it to other multikey access file structures.