Beginning Oracle Database 11g Administration From Novice to Professional

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CHAPTER 17 SQL TUNING
Identifying Inefficient SQL Statements
When an application is performing poorly or a batch job takes a long time, we have to
identify SQL statements that are consuming a lot of resources and are candidates for tuning.
The simplest way to do this is to watch the operation of the database by using a GUI
tool such as Enterprise Manager or SQL Developer. In Figure 17-1, you can see a query
being run by .
Figure 17-1. Using SQL Developer to monitor sessions
A systematic way of identifying tuning candidates in a batch job is to trace the job. If
you ask Oracle to trace a job, it records SQL statements and execution details in a trace
file. The simplest way to start tracing a session is to use Enterprise Manager or SQL Developer
as in Figure 17-1. You can also use the command as in the
following example:
You can then use the tool to summarize the information in a more readable
form, as in Listing 17-1. You can see that a particular statement was executed 163 times—
execution statistics are also displayed. In this case, the number of logical reads—the
number of buffers gotten for consistent read—is zero because the information is coming
from dynamic performance tables, not from actual database tables.