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From Bill Au <bill.w...@gmail.com>
Subject Re: Cassandra crashed - possible JMX threads leak
Date Tue, 26 Oct 2010 15:28:50 GMT
I would be happy to submit a patch but is it a bit more trickier than simply
calling JMXConenctor.close().  NodeProbe's use of the JMXConnector is not
exposed in its API  The JMX connection is created in NodeProbe's
constructor.  Without changing the API, the only place to call close() would
be in NodeProbe's finalize().  I am not sure if that's the best thing to
do.  I think this warrant a discussion on the developer mailing list.  I
will start an new mail thread there.

Anyways, I am still trying to understand why the JMX server connection
timeout threads pile up rather quickly when I restart a node in a live
cluster.  I took a look at the Cassandra source and see that NodeProbe is
the only place that creates and uses a JMX connection.  And NobeProbe is
only used by the tools.  So it seems that there is another JMX thread leak
in Cassandra.

Bill

On Fri, Oct 22, 2010 at 4:33 PM, Jonathan Ellis <jbellis@gmail.com> wrote:

> Is the fix as simple as calling close() then?  Can you submit a patch for
> that?
>
> On Fri, Oct 22, 2010 at 2:49 PM, Bill Au <bill.w.au@gmail.com> wrote:
> > Not with the nodeprobe or nodetool command because the JVM these two
> > commands spawn has a very short life span.
> >
> > I am using a webapp to monitor my cassandra cluster.  It pretty much uses
> > the same code as NodeCmd class.  For each incoming request, it creates an
> > NodeProbe object and use it to get get various status of the cluster.  I
> can
> > reproduce the Cassandra JVM crash by issuing requests to this webapp in a
> > bash while loop.  I took a deeper look and here is what I discovered:
> >
> > In the webapp when NodeProbe creates a JMXConnector to connect to the
> > Cassandra JMX port, a thread
> > (com.sun.jmx.remote.internal.ClientCommunicatorAdmin$Checker) is created
> and
> > run in the webapp's JVM.  Meanwhile in the Cassamdra JVM there is a
> > com.sun.jmx.remote.internal.ServerCommunicatorAdmin$Timeout thread to
> > timeout remote JMX connection.  However, since NodeProbe does not call
> > JMXConnector.close(), the JMX client checker threads remains in the
> webapp's
> > JVM even after the NobeProbe object has been garbage collected.  So this
> JMX
> > connection is still considered open and that keeps the JMX timeout thread
> > running inside the Cassandra JVM.  The number of JMX client checker
> threads
> > in my webapp's JVM matches up with the number of JMX server timeout
> threads
> > in my Cassandra's JVM.  If I stop my webapp's JVM,
> > all the JMX server timeout threads in my Cassandra's JVM all disappear
> after
> > 2 minutes, the default timeout for a JMX connection.  This is why the
> > problem cannot be reproduced by nodeprobe or nodetool.  Even though
> > JMXConnector.close() is not called, the JVM exits shortly so the JMX
> client
> > checker thread do not stay around.  So their corresponding JMX server
> > timeout thread goes away after two minutes.  This is not the case with my
> > weabpp since its JVM keeps running, so all the JMX client checker threads
> > keep running as well.  The threads keep piling up until it crashes
> > Casssandra's JVM.
> >
> > In my case I think I can change my webapp to use a static NodeProbe
> instead
> > of creating a new one for every request.  That should get around the
> leak.
> >
> > However, I have seen the leak occurs in another situation.  On more than
> one
> > occasions when I restarted one node in a live multi-node clusters, I see
> > that the JMX server timeout threads quickly piled up (number in the
> > thousands) in Cassandra's JVM.  It only happened on a live cluster that
> is
> > servicing read and write requests.  I am guessing the hinted hand off
> might
> > have something to do with it.  I am still trying to understand what is
> > happening there.
> >
> > Bill
> >
> >
> > On Wed, Oct 20, 2010 at 5:16 PM, Jonathan Ellis <jbellis@gmail.com>
> wrote:
> >>
> >> can you reproduce this by, say, running nodeprobe ring in a bash while
> >> loop?
> >>
> >> On Wed, Oct 20, 2010 at 3:09 PM, Bill Au <bill.w.au@gmail.com> wrote:
> >> > One of my Cassandra server crashed with the following:
> >> >
> >> > ERROR [ACCEPT-xxx.xxx.xxx/nnn.nnn.nnn.nnn] 2010-10-19 00:25:10,419
> >> > CassandraDaemon.java (line 82) Uncaught exception in thread
> >> > Thread[ACCEPT-xxx.xxx.xxx/nnn.nnn.nnn.nnn,5,main]
> >> > java.lang.OutOfMemoryError: unable to create new native thread
> >> >         at java.lang.Thread.start0(Native Method)
> >> >         at java.lang.Thread.start(Thread.java:597)
> >> >         at
> >> >
> >> >
> org.apache.cassandra.net.MessagingService$SocketThread.run(MessagingService.java:533)
> >> >
> >> >
> >> > I took threads dump in the JVM on all the other Cassandra severs in my
> >> > cluster.  They all have thousand of threads looking like this:
> >> >
> >> > "JMX server connection timeout 183373" daemon prio=10
> >> > tid=0x00002aad230db800
> >> > nid=0x5cf6 in Object.wait() [0x00002aad7a316000]
> >> >    java.lang.Thread.State: TIMED_WAITING (on object monitor)
> >> >         at java.lang.Object.wait(Native Method)
> >> >         at
> >> >
> >> >
> com.sun.jmx.remote.internal.ServerCommunicatorAdmin$Timeout.run(ServerCommunicatorAdmin.java:150)
> >> >         - locked <0x00002aab056ccee0> (a [I)
> >> >         at java.lang.Thread.run(Thread.java:619)
> >> >
> >> > It seems to me that there is a JMX threads leak in Cassandra.
> NodeProbe
> >> > creates a JMXConnector but never calls its close() method.  I tried
> >> > setting
> >> > jmx.remote.x.server.connection.timeout to 0 hoping that would disable
> >> > the
> >> > JMX server connection timeout threads.  But that did not make any
> >> > difference.
> >> >
> >> > Has anyone else seen this?
> >> >
> >> > Bill
> >> >
> >>
> >>
> >>
> >> --
> >> Jonathan Ellis
> >> Project Chair, Apache Cassandra
> >> co-founder of Riptano, the source for professional Cassandra support
> >> http://riptano.com
> >
> >
>
>
>
> --
> Jonathan Ellis
> Project Chair, Apache Cassandra
> co-founder of Riptano, the source for professional Cassandra support
> http://riptano.com
>

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