11g Integration of SQL Plan Management with Automatic SQL Tuning Oracle 11g New Features Tips by Donald BurlesonJune 29, 2015

Oracle 11g New Features Tips

The next step is also already implemented in Oracle database 11g. It is called Automatic SQL Tuning. With this feature enabled, Oracle runs an automatic task job every night in a maintenance window. It is also called Automatic SQL Tuning Advisor and searches for high load SQL, then starts automatically tuning the worst statements. Output could be recommendations about missing indexes for instance, and if allowed, automatic implementation of automatically created and tested SQL Profiles. This is not enabled by default. The job would then feed the SQL plan baselines with the plans from the automatically created and implemented SQL profiles and mark the new plans as ENABLED and ACCEPTED.

The SYS_AUTO_SQL_TUNING_TASK runs in the daily maintenance window and can be monitored with the data dictionary view DBA_ADVISOR_EXECUTIONS. The Automatic SQL Tuning job can be managed via the built in package DBMS_AUTO_TASK_ADMIN. The choice can also be made to not fix the plan in the new baseline and allow the optimizer from now on to evolve the plan baseline and use new best cost plans found for the statement, but only if it has been verified that they do not cause performance regression.

If the Automatic Tuning job finds a better plan and implements a SQL Profile automatically and automatic implementation of SQL Profiles has been allowed, it adds the new plan to the plan baseline but does not verify existing unaccepted plans. The criteria for automatic implementation of SQL profiles and feeding new plans into the plan baselines would be that the improvement of the new plan sums up to at least three times less cost (sum of CPU and I/O time). Only High Load Repeatable SQL is automatically tuned. Who cares about low load SQL?

The syntax to enable Automatic SQL Tuning is as follows:

LUTZ AS SYSDBA @ prod11g1 SQL> BEGIN

dbms_sqltune.set_tuning_task_parameter('SYS_AUTO_SQL_TUNING_TASK', 'ACCEPT_SQL_PROFILES', 'TRUE');

END;

% The default value for ACCEPT_SQL_PROFILES is FALSE!

It is also possible to adjust the Automatic SQL Tuning Task in the graphical interface:

Figure 29:  Automatic SQL Tuning Settings Screen

For more detailed information on Automatic SQL Tuning, please refer to Chapter 6 in this book.

There have been multiple techniques to control execution plans available for quite a while. These include hints, stored outlines and SQL profiles. What all of these methods have in common is that they need manual intervention since they are fixed remedies which do not adjust to changed demands automatically. Also, they can only be used after the problem has actually occurred, so they are reactive methods.

SQL Plan management is a proactive approach to possible upcoming problems and can help to ensure that performance regression is prevented and only execution plans which are significantly better than the ?well tuned and well known? plans can be used by the optimizer.

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