You find today’s performance of your production database to be the best ever. Therefore, you want
to be notified in the future whenever the performance degrades by 10% of today’s performance.
What is the first step that you would take to ensure this?
A.
create baseline metrics for today’s performance
B.
write the current database metrics to a database table and create a trigger to compare with
future database statistics
C.
write the current database metrics to a flat file and create an operating script to compare with
future database statistics
D.
write the current database metrics to a database table and create a procedure to compare with
future database statistics
E.
write the current database metrics to a database table and submit a job using DBMS_JOB to
compare with future database statistics
Creating a baseline allowed a specified range of snapshots to be retained, regardless of the AWR retention policy, and used for performance comparisons.
Originally, the DBMS_WORKLOAD_REPOSITORY package included a single CREATE_BASELINE procedure allowing you to define baselines using specific snapshot IDs. It now includes overloaded procedures and functions allowing baselines to be created using start and end times, which are used to estimate the relevant snapshot IDs.
When SQL plan management is enabled, the optimizer stores generated execution plans in a special repository, the SQL management base. All stored plans for a specific SQL statement are said to be part of a plan history for that SQL statement.
Some of the plans in the history can be marked as “accepted.”When the SQL statement is reparsed, the optimizer considers only the accepted plans in the history. This set of accepted plans for that SQL statement is called a SQL plan baseline , or baseline for short.
The optimizer still tries to generate a better plan, however. If the optimizer does generate a new plan, it adds it to the plan history but does not consider it while reparsing the SQL, unless the new plan is better than all the accepted plans in the baseline.