Access Methods

Abstract

In this chapter we will look at the primary methods that the runtime engine uses to access data held in the database. In each case we provide basic details of the algorithm used, the execution plan operation names, and the hint that can be used to explicitly specify the access method. I will begin by a discussion of what a ROWID is and the various ways it can be used to access a table. This will lead nicely into two sections that discuss the various ways in which B-tree and bitmap indexes can be used to generate ROWIDs. The last three sections in this chapter discuss the much maligned full table scan, the little understood TABLE and XMLTABLE operators, and for completeness cluster access, which most people will never need to use.