Switch the new undo tablespace in the automatic undo tablespace mode

After switching the new undo tablespace In the Undo automatic tablespace mode, you must drop the old undo tablespace, However, because the activity is not completely completed during the switchover, As a result, the error "ORA-30013: Restoring tablespace 'undotbs3' is currently in use" is reported when the pilot drops the old undo tablespace. The solution is as follows: 1. Confirm the rollback segment number used by the event
Select xidusn from V $ transaction;
2. Confirm the SID and serial corresponding to the activity event #
Select a. Sid, A. Serial # from V $ session A, V $ transaction B Where a. taddr = B. ADDR;
3. Run the alter system kill session command to kill related active sessions.   4. rollback segments queried in step 1 of offline In this step, you need to modify the implicit parameter _ smu_debug_mode and change its value to 4. This step aims to enable operations in the Undo manual mode, for example, the offline rollback segment or the deletion rollback segment. Run alter rollback segment "_ syssmun $" offline; (where N is the rollback segment number queried in step 1)   5. The drop undo tablespace command can be executed normally.
conclusion: the key here is to ensure that all pending items in the old tablespace have ended, therefore, if you do not manually kill related active sessions, an error will be reported if you perform offline or drop operations on the rollback segments of the active sessions.