Oracle Enterprise Manager 13c Cloud Control Agent Shows Agent Unreachable Status

One of client’s OEM agent is working fine, but OEM console show “Agent Unreachable’ for this agent and all the other targets monitored by this agent.

Agent Unreachable

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The agent is overloaded [current requests: 128]

Java layer deadlock —“Dead Lock detected!!”, bounce the agent, and then everything is working fine.

SITUATION

The following alerts are received from racnode1 -“The agent is overloaded [current requests: 128]”

From: oracle 
Sent: Friday, 4 August 2017 7:07 PM
Cc: 
Subject: EM Event: Warning: racnode1 - Agent Unreachable (REASON = The agent is overloaded [current requests: 128]). Host is reachable.

...
..
.
Categories=Availability 
Message=Agent Unreachable (REASON = The agent is overloaded [current requests: 128]). Host is reachable. 
Severity=Warning 
Event reported time=Aug 4, 2017 7:06:27 PM AEST
...
..
.

INVESTIGATING

1)   Check agent status

Agent is running
Agent upload is not working
Agent reload is not working
OMS heartbeat is not working

$ emctl status agent
Oracle Enterprise Manager Cloud Control 12c Release 5
Copyright (c) 1996, 2015 Oracle Corporation. All rights reserved.
---------------------------------------------------------------
Agent Version : 12.1.0.5.0
OMS Version : 13.2.0.0.0
Protocol Version : 12.1.0.1.0
..
.
Last Reload : 2017-08-04 11:28:59
Last successful upload : 2017-08-04 14:51:03  <--- 5 hours ago
Last attempted upload : 2017-08-04 14:51:03
..
.
Last attempted heartbeat to OMS : 2017-08-04 14:50:23
Last successful heartbeat to OMS : 2017-08-04 14:50:23
Next scheduled heartbeat to OMS : 2017-08-04 14:51:23

2) Upload agent
$ emctl upload agent
Oracle Enterprise Manager Cloud Control 12c Release 5
Copyright (c) 1996, 2015 Oracle Corporation. All rights reserved.
---------------------------------------------------------------
EMD upload error:The agent is overloaded [current requests: 128]
3) Reload agent
$ emctl reload agent
Oracle Enterprise Manager Cloud Control 12c Release 5
Copyright (c) 1996, 2015 Oracle Corporation. All rights reserved.
---------------------------------------------------------------
EMD reload error:The agent is overloaded [current requests: 128]
4) “emagent_perl.trc” file has no information updated since agent restarted
5) Check “gcagent.log”

Java layer deadlock —“Dead Lock detected!!”

2017-08-04 19:28:59,071 [43:GCThread-13] ERROR -
Dead Lock detected!!
Participating threads:Thread Info Dump:
=================
"HTTP Listener-3592 - /emd/main/ (~Task-free~ OMS.pbs@16398@omsnode=>[150183756670001])" tid=3592 WAITING
 > Accumulated wait time (msec): 1372208 (1 times)

"HTTP Listener-2141 - /emd/main/ (~Task-free~ OMS.pbs@13103@omsnode=>[150182243190001])" tid=2141 BLOCKED
 > Accumulated wait time (msec): 11036289 (76 times)
 > Accumulated blocked time (msec): 16506994 (4 times)

"oracle.dfw.impl.incident.DiagnosticsDataExtractorImpl - Incident Dump Executor (created: Fri Aug 04 14:51:06 EST 2017)" tid=3088 BLOCKED
 > Accumulated blocked time (msec): 16672145 (7 times)

"HTTP Listener-1022 - /emd/main/ (~Task-free~ OMS.pbs@16398@omsnode=>[150181021899001])" tid=1022 WAITING
 > Accumulated wait time (msec): 28746227 (37 times)
 > Accumulated blocked time (msec): 133 (12 times)

"HTTP Listener-1078 - /emd/main/ (DispatchRequests OMS.console@16398@omsnode=>[150181015881006])" tid=1078 WAITING
 > Accumulated wait time (msec): 28719225 (44 times)

=================
Thread Info Dump:
=================
"HTTP Listener-3592 - /emd/main/ (~Task-free~ OMS.pbs@16398@omsnode=>[150183756670001])" tid=3592 WAITING
 sun.misc.Unsafe.park(Native Method)
 - waiting on <0x149717ec> (a java.util.concurrent.locks.ReentrantLock$NonfairSync), which is owned by "HTTP Listener-2141 - /emd/main/ (~Task-free~ OMS.pbs@13103@omsnode=>[150182243190001])" (tid=2141)
 java.util.concurrent.locks.LockSupport.park(LockSupport.java:156)
 java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:811)
 java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:842)
 java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1178)
 java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLock.java:186)
...
..
.

SOLUTION

1) Stop agent
$ emctl stop agent
Oracle Enterprise Manager Cloud Control 12c Release 5
Copyright (c) 1996, 2015 Oracle Corporation. All rights reserved.
Stopping agent ...
 stopped.
2) Start agent
$ emctl start agent
Oracle Enterprise Manager Cloud Control 12c Release 5
Copyright (c) 1996, 2015 Oracle Corporation. All rights reserved.
Starting agent ............................................ started.
3) Upload agent successfully
$ emctl upload agent
Oracle Enterprise Manager Cloud Control 12c Release 5
Copyright (c) 1996, 2015 Oracle Corporation. All rights reserved.
---------------------------------------------------------------
EMD upload completed successfully
4) Reload agent successfully
$ emctl reload agent
Oracle Enterprise Manager Cloud Control 12c Release 5
Copyright (c) 1996, 2015 Oracle Corporation. All rights reserved.
---------------------------------------------------------------
EMD reload completed successfully
5)Check agent status successfully
$ emctl status agent
...
..
Last attempted heartbeat to  OMS : 2017-08-04 19:53:31
Last successful heartbeat to OMS : 2017-08-04 19:53:31
Next scheduled heartbeat to  OMS : 2017-08-04 19:54:32

---------------------------------------------------------------
Agent is Running and Ready