oracle does not automatically create a snapshot, you can not collect awr report (mmon, mmnl process)

Solution:
1, restart Example
2 without restarting instance, the database is arranged to restricted session mode
ALTER System enable restricted session;
ALTER System disable restricted session;
    disposed restricted session mode, no effect on dba privileges, ordinary users can not connect to the database , need to grant permission to connect to the database restricted session, the average user will not affect the existing link.