20.1. Introduction

During the early 1980s, the UNIX System was considered a hostile environment for running multiuser database systems. (See Stonebraker [1981] and Weinberger [1982].) Earlier systems, such as Version 7, did indeed present large obstacles, since they did not provide any form of IPC (other than half-duplex pipes) and did not provide any form of byte-range locking. Many of these deficiencies were remedied, however. By the late 1980s, the UNIX System had evolved to provide a suitable environment for running reliable, multiuser database systems. Since then, numerous commercial firms have offered these types of database systems.

In this chapter, we develop a simple, multiuser database library of C functions that any program can call to fetch and store records in a database. This library of C functions is usually only one part of a complete database system. We do not develop the other pieces, such as a query language, leaving these items to the many textbooks on database systems. Our interest is the UNIX System interface a database library requires and how that interface relates to the topics we've already covered (such as recordbyte-rangelocking, in Section 14.3).