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About the SQL Tuning Advisor
The SQL Tuning Advisor examines a given SQL statement or a set of SQL statements
and provides recommendations to improve efficiency. It can make various types of
recommendations, such as creating a SQL profile (a collection of information that
enables the query optimizer to create an optimal execution plan for a SQL statement),
restructuring SQL statements, and refreshing optimizer statistics. SQL Tuning Advisor
also enables you to pick an alternative execution plan (stored in AWR) from the past
and use it with the SQL statement, and can also recommend degree of parallelism
profiles. EM Express enables you to accept and implement many of these
recommendations with just a few mouse clicks.
You use the SQL Tuning Advisor to tune a single SQL statement or multiple SQL
statements. Typically, you run the SQL Tuning Advisor in response to an ADDM
performance finding that recommends its use. You can also run it periodically on the
most resource-intensive SQL statements, and on a SQL workload.
When tuning multiple SQL statements, the SQL Tuning Advisor does not recognize
interdependencies between the SQL statements. It solves SQL performance problems
by identifying problems with individual SQL statements, such as a poorly performing
optimizer plan or the mistaken use of certain SQL structures.
You can run the SQL Tuning Advisor against the following sources:
■ Activity—The most resource-intensive SQL statements executed during the last
hour that appear on the Activity tab of the Performance Hub that might have
caused recent performance problems.
■ Historical SQL—A SQL statement from the last day, week, or month that appear
on the Activity tab of the Performance Hub when one of the historical settings is
selected in the Select Time Period field. Use this option for proactive tuning of
SQL statements.
■ Historical SQL from ADDM—A resource-intensive SQL statement from an ADDM
task that you discover when analyzing a task on the ADDM tab of the
Performance Hub.
■ SQL statement in SQL Tuning Advisor—A resource-intensive SQL statement that
appears as a tuning task in SQL Tuning Advisor.
■ SQL tuning sets (STS)—A set of SQL statements you provide. An STS can be
created from SQL statements captured by AWR snapshots or from a SQL
workload.
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