aix+Oracle10g环境，同一主机上有多套数据库，发现有两套库的AWR快照不能定时生成；
现象是：手动执行exec dbms_workload_repository.create_snapshot;可以生成快照，或者kill mmon进程后，MMON进程启动时能生成一个快照，之后无法生成，查看mmnl进程trace,可以发现里面是有数据的；
参考MOS文档Troubleshooting: Missing Automatic Workload Repository (AWR) Snapshots and Other Collection Issues (文档 ID 1301503.1)，按文档中的排查顺序也未查到原因； 通过查看进程的等待事件，发现等待事件是：wait for EMON to process ntfns。
最终查到是原因是OEM Agent，关闭OEM Agent后，MMON进程不再出现此等待事件，后续AWR快照生成恢复正常。
参考MOS文档：Slow Response OEM Agent Causes MMON Hung with "EMON to process ntnfs" (文档 ID 2308245.1) 其它AWR未生成排查思路参考以前写的
主要排查过程信息：
1.MMON进程的异常等待事件：
EVENT PROGRAM SID
------------------------------ ------------------------- ----------
EMON idle wait (EMN0) 1629
wait for EMON to process ntfns (MMON) 1645
2.关闭oem agent
ABC123:/u01/oracle/agent12c/agent_inst/bin> ./emctl stop agent
Oracle Enterprise Manager Cloud Control 12c Release 5
Copyright (c) 1996, 2015 Oracle Corporation. All rights reserved.
Stopping agent ... stopped.
-rw-r----- 1 oracle oinstall 995984 Jan 09 17:18 emdctlj.log
-rw-r----- 1 oracle oinstall 3326 Jan 09 17:18 emagent.nohup
ABC123:/u01/oracle/agent12c/agent_inst/sysman/log>
3.查看MMON进程是否有异常等待事件
SQL> select event,PROGRAM,sid from v$session where event like '%EMON%';
EVENT PROGRAM SID
------------------------------ ------------------------- ----------
EMON idle wait (EMN0) 1629
4.查看AWR快照生成情况
SQL> @?/rdbms/admin/awrrpt.sql
Current Instance
~~~~~~~~~~~~~~~~
DB Id DB Name Inst Num Instance
----------- ------------ -------- ------------
4112577184 test123 1 test123
………………
Enter value for num_days:
Listing all Completed Snapshots
Snap
Instance DB Name Snap Id Snap Started Level
------------ ------------ --------- ------------------ -----
test123 test123 58503 08 Jan 2018 12:40 1
58504 09 Jan 2018 16:21 1
58505 09 Jan 2018 17:18 1
