OCP-1Z0-053-V12.02-80题

80.Which two statements regarding a SQL profile are true? (Choose two.)

A. It is built by Automatic Tuning Optimizer.

B. It cannot be stored persistently in the data dictionary.

C. It can be used by the query optimizer automatically.

D. It can be created manually by using the CREATE PROFILE command.

Answer: AC

答案解析：

参考：http://docs.oracle.com/cd/E11882_01/server.112/e41573/sql_tune.htm#PFGRF94873

SQL Profile Creation

When you accept a profile, the database creates the profile and stores it persistently in the data dictionary. If a user issues a statement for which a profile has been built, then the query optimizer (in normal mode) uses both the environment and the SQL profile to build a well-tuned plan.

As a rule of thumb, accept a SQL profile recommended by SQL Tuning Advisor. If both an index and a SQL profile are recommended, then either use both or use the SQL profile only. If you create an index, then the optimizer may need the profile to pick the new index.

In some situations, SQL Tuning Advisor may find an improved serial plan in addition to an even better parallel plan. In this case, the advisor recommends both a standard and a parallel SQL profile, enabling you to choose between the best serial and best parallel plan for the statement. Accept a parallel plan only if the increase in response time is worth the decrease in throughput