{ "date": "2014-07-18T02:24:00", "slug": "oracle-em-agent-12c-thread-leak-on-rac", "link": "https://www.dbi-services.com/blog/oracle-em-agent-12c-thread-leak-on-rac/", "title": { "rendered": "Oracle EM agent 12c thread leak on RAC" }, "content": { "rendered": "

By Franck Pachot

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\nIn a previous post about nproc limit, I wrote that I had to investigate the nproc limit with the number of threads because my Oracle 12c EM agent was having thousands of threads. This post is a short feedback about this issue and the way I have found the root cause. It concerns the enterprise manager agent 12c on Grid Infrasctructure >= 11.2.0.2

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NLWP

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The issue was:

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ps -o nlwp,pid,lwp,args -u oracle | sort -n\nNLWP   PID   LWP COMMAND\n   1  8444  8444 oracleOPRODP3 (LOCAL=NO)\n   1  9397  9397 oracleOPRODP3 (LOCAL=NO)\n   1  9542  9542 oracleOPRODP3 (LOCAL=NO)\n   1  9803  9803 /u00/app/oracle/product/agent12c/core/12.1.0.3.0/perl/bin/perl /u00/app/oracle/product/agent12c/core/12.1.0.3.0/bin/emwd.pl agent /u00/app/oracle/product/agent12c/agent_inst/sysman/log/emagent.nohup\n  19 11966 11966 /u00/app/11.2.0/grid/bin/oraagent.bin\n1114  9963  9963 /u00/app/oracle/product/agent12c/core/12.1.0.3.0/jdk/bin/java ... emagentSDK.jar oracle.sysman.gcagent.tmmain.TMMain\n
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By default ps has only one entry per process, but each processes can have several threads – implemented on linux as light-weight process (LWP). Here, the NLWP column shows that I have 1114 threads for my EM 12c agent – and it was increasing every day until it reached the limit and the node failed (‘Resource temporarily unavailable’).

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The first thing to do is to know what those threads are. The ps entries do not have a lot of information, but I discovered jstack which every java developer should know, I presume. You probably know that java has very verbose (lengthy) stack traces. Jstack was able to show me thousands of them in only one command:

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Jstack

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$ jstack 9963\n2014-06-03 13:29:04\nFull thread dump Java HotSpot(TM) 64-Bit Server VM (20.14-b01 mixed mode):\n\n\"Attach Listener\" daemon prio=10 tid=0x00007f3368002000 nid=0x4c9b waiting on condition [0x0000000000000000]\n   java.lang.Thread.State: RUNNABLE\n\n\"CRSeOns\" prio=10 tid=0x00007f32c80b6800 nid=0x3863 in Object.wait() [0x00007f31fe11f000]\n   java.lang.Thread.State: TIMED_WAITING (on object monitor)\n\tat java.lang.Object.wait(Native Method)\n\tat oracle.eons.impl.NotificationQueue.internalDequeue(NotificationQueue.java:278)\n\t- locked  (a java.lang.Object)\n\tat oracle.eons.impl.NotificationQueue.dequeue(NotificationQueue.java:255)\n\tat oracle.eons.proxy.impl.client.base.SubscriberImpl.receive(SubscriberImpl.java:98)\n\tat oracle.eons.proxy.impl.client.base.SubscriberImpl.receive(SubscriberImpl.java:79)\n\tat oracle.eons.proxy.impl.client.ProxySubscriber.receive(ProxySubscriber.java:29)\n\tat oracle.sysman.db.receivelet.eons.EonsMetric.beginSubscription(EonsMetric.java:872)\n\tat oracle.sysman.db.receivelet.eons.EonsMetricWlm.run(EonsMetricWlm.java:139)\n\tat oracle.sysman.gcagent.target.interaction.execution.ReceiveletInteractionMgr$3$1.run(ReceiveletInteractionMgr.java:1401)\n\tat java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:895)\n\tat java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:918)\n\tat oracle.sysman.gcagent.util.system.GCAThread$RunnableWrapper.run(GCAThread.java:184)\n\tat java.lang.Thread.run(Thread.java:662)\n...\n
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CRSeOns

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I don’t paste all of them here. We have the ‘main’, we have a few GCs and ‘Gang workers’ which are present in all JVMs and we have a few enterprise manager threads. And what was interesting was that I had thousands of “CRSeOns” that seemed to be increasing.

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Some guesses: I’m on RAC, and I have a ‘ons’ resource and the EM agent tries to subscribe to it. Goggle search returned nothing, and that’s the reason I put that in a blog post now. Then I searched MOS, and bingo, there is a note: Doc ID 1486626.1. It has nothing to do with my issue, but has an interesting comment in it:

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In cluster version 11.2.0.2 and higher, the ora.eons resource functionality has been moved to EVM. Because of this the ora.eons resource no longer exists or is controlled by crsctl.

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It also explains how to disable EM agent subscription:

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emctl setproperty agent -name disableEonsRcvlet -value true
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I’m in 11.2.0.3 and I have thousands of threads related to a functionality that doesn’t exist anymore. And that leads to some failures in my 4 nodes cluster.

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The solution was simple: disable it.

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For a long time I have seen a lot of memory leaks or CPU usage leaks related to the enterprise manager agent. With this new issue, I discovered a thread leak and I also faced a SR leak when trying to get support for the ‘Resource temporarily unavailable’ error, going back and forth between OS, Database, Cluster and EM support teams…

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