Explanation/Reference:
Explanation:
With adaptive SQL plan management, DBAs no longer have to manually run the verification or evolve process for non-accepted plans. When automatic SQL tuning is in COMPREHENSIVE mode, it runs a verification or evolve process for all SQL statements that have non-accepted plans during the nightly maintenance window. If the non-accepted plan performs better than the existing accepted plan (or plans) in the SQL plan baseline, then the plan is automatically accepted and becomes usable by the optimizer.
After the verification is complete, a persistent report is generated detailing how the non-accepted plan performs compared to the accepted plan performance. Because the evolve process is now an AUTOTASK, DBAs can also schedule their own evolve job at end time.
Note:
* The optimizer is able to adapt plans on the fly by predetermining multiple subplans for portions of the plan.
* Adaptive plans, introduced in Oracle Database 12c, enable the optimizer to defer the final plan decision for a statement until execution time. The optimizer instruments its chosen plan (the default plan) with statistics collectors so that it can detect at runtime, if its cardinality estimates differ greatly from the actual number of rows seen by the operations in the plan. If there is a significant difference, then the plan or a portion of it will be automatically adapted to avoid suboptimal performance on the first execution of a SQL statement.