|Lesson 5||The EXPLAIN PLAN utility |
|Objective||Understand the Basic Functions of the Oracle EXPLAIN PLAN Utility|
View access path to data
More than any other tool, the EXPLAIN PLAN utility is the most indispensable.
In fact, all of the other Oracle tools rely on the EXPLAIN PLAN utility to allow the DBA to view the access path to the data. We have no hope of tuning a SQL query until
we can see how it is accessing the database, and the EXPLAIN PLAN utility makes the access path visible.
The EXPLAIN PLAN utility can be invoked directly on the UNIX server with the EXPLAIN PLAN command syntax, or it can be invoked from Oracle SQL analyze client software.
Oracle Tuning - Definitive Reference
As we noted in an earlier lesson, it is never clear from looking at an SQL statement how the database will be accessed.
To illustrate, consider the following SQL statement presented in the Slide Show.