生成awr报告的过程中，发生awr报告没有快照，并返回ORA-20200错误。
查看dba_hist_active_session_history发现有数据，判断mmon和mmnl后台进程的问题，故需要重新启动mmon和mmnl后台进程
方法一：
重启数据库
方法二：
启用restricted模式，再立马禁用：
alter system enable restricted session;
alter system disable restricted session;
alter日志
Stopping background process MMNL Sat Jan 11 22:07:07 2020 Stopping background process MMON Sat Jan 11 22:07:39 2020 Background process MMON not dead after 30 seconds Sat Jan 11 22:07:39 2020 Killing background process MMON Sat Jan 11 22:08:15 2020 Starting background process MMON MMON started with pid=19, OS id=2957544 Sat Jan 11 22:08:15 2020 Starting background process MMNL MMNL started with pid=55, OS id=4960290 Sat Jan 11 22:08:15 2020 ALTER SYSTEM enable restricted session; Sat Jan 11 22:08:15 2020 ALTER SYSTEM disable restricted session;