Database Reference
In-Depth Information
Figure 11-5.
Main steps carried out during the execution of a SQL statement
Here are the steps in detail:
A.
The user sends a SQL statement to be executed to the SQL engine.
B.
The SQL engine asks the query optimizer to provide an execution plan.
C.
The query optimizer gets the system statistics, the object statistics related to the
objects referenced by the SQL statement, the SQL profile, and the initialization
parameters that set up the execution environment.
D.
The query optimizer analyzes the SQL statement and generates the execution plan.
E.
The execution plan is passed to the SQL engine.
F.
The SQL engine executes the SQL statement.
The next sections describe in detail the central steps carried out during the generation and utilization of SQL
profiles. Special focus is given to the steps that involve the user. Let's start by describing the SQL Tuning Advisor.
SQL Tuning Advisor
The core interface of the SQL Tuning Advisor is available through the
dbms_sqltune
package. In addition, a graphical
interface is integrated in Enterprise Manager. Both interfaces allow you to execute a
tuning task.
They also allow you
to review the resulting advice and to accept it. I don't show you here how the graphical user interface works because
it's more important to understand what goes on behind the scenes.
