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From Isaac Gonzalez <>
Subject RE: tomcat 6 refuses mod_jk connections after server runs for a couple of days
Date Sat, 01 Mar 2014 05:36:08 GMT

From: Christopher Schultz []
Sent: Friday, February 28, 2014 11:38 AM
To: Tomcat Users List
Subject: Re: tomcat 6 refuses mod_jk connections after server runs for a couple of days

Hash: SHA256


On 2/27/14, 5:40 PM, Konstantin Kolinko wrote:
> 2014-02-28 2:06 GMT+04:00 Isaac Gonzalez
> <>:
>> Hi Christopher(and Konstantin), attached is a couple of thread
>> dumps of when we experienced the issue again today. I also
>> noticed we get this message right before the problem occurs: Feb
>> 27, 2014 12:47:15 PM
>> org.apache.tomcat.util.threads.ThreadPool$ControlRunnable run
>> SEVERE: Caught exception (java.lang.OutOfMemoryError: unable to
>> create new native thread) executing
>> org.apache.jk.common.ChannelSocket$SocketAcceptor@177ddea,
>> terminating thread
> That explains why a connection cannot be accepted.
> I wonder are you hitting an "ulimit" limit, or there is just not
> enough free memory to allocate stack area for a new thread (which
> size is set by -Xss option to java executable).
> Your thread dumps contain 149 threads each.

While it does explain why one (Tomcat) server would become
unresponsive, it doesn't really explain why the entire cluster would
become unresponsive.

Issac, are you using sticky-sessions or anything like that, or does
your load-balancing mod_jk configuration choose arbitrarily between a
backend server? You initially gave an abridged configuration, so I
can't tell.
           As you indicate below, I am not clustering. There is only one backend tomcat.

>> After the "split", did both Tomcats appear to lock-up
>> simultaneously, or did only one of them have a problem and the
>> other one stayed up?
> Isaac: They all appear to lock-up simultaneously, if users try to
> access that JK mount point.
> [...]
> Isaac: I am not load-balancing the tomcat servers...I only have
> one...I do "load balance" the apache front end servers via dns
> round-robin....

Oh, you only have a single back-end server? Well, then that why they
"all" go down at once, so you seem to have found your problem: the
server itself is going down because you don't have enough resources to
keep it up.

      Indeed I have! Seems like I underallocated server memory...the machine had only 8 Gigs
with 7 tomcat instances running that all had up to a maximum of 2 gigs of maximum memory heap
size, plus OS stuff running, RabbitMQ, and other things. I am wondering though if something
else could be the underlying root cause of this issue, or was I simply under allocating memory..such
as connections not being closed, either by the client mod_jk connector, or the db connector...We'll
see in the next few days I guess....
thanks again Chris, you and Konstantin pointed me to the issue...


- -chris
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