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From Dante Bell <>
Subject Re: Urgent: Tomcat 6.0.20 on Solaris 10 Reaches max threads and is non responsive
Date Fri, 05 Aug 2011 15:56:51 GMT

Like I said, I'm an OS/HW guy, never looked at java b4!

They are saying that the load test has 20 'connections' so I'm guessing
that's the 20 STMs.

Now, is this a fixable thing within the Java stack? Or is it an
application limitation?


On 08/05/2011 11:12 AM, Mark Thomas wrote:
> On 05/08/2011 15:34, Dante Bell wrote:
>> Hi,
>> I'm running out of ideas on what to try for this customer. Their load
>> tests show that Tomcat is getting to a point where it no longer services
>> requests.
> Let me guess. It is fine for low loads but as soon as the load goes
> above a certain number (maybe around 20 concurrent users?) then
> everything starts going wrong?
>> Thread dumps show most threads in a wait state, but some are
>> runnable. I'm suspecting GC is the issue,
> On what basis? The thread dump clearly shows a different problem.
>> but in analyzing the logs it
>> shows the longest pause was 15 seconds, but that only happened once, and
>> most of the stats look OK to me.
> That would suggest that it isn't GC then wouldn't it.
>> Details can be found on my blog:
> All the information needed to diagnose this issue is in the thead dump.
> If you take a look at the first thread that is blocked:
> "TP-Processor40745" daemon prio=3 tid=0x03831400 nid=0xa888 in
> Object.wait() [0x2cd2f000..0x2cd2f870]
>    java.lang.Thread.State: WAITING (on object monitor)
> 	at java.lang.Object.wait(Native Method)
> 	at java.lang.Object.wait(
> 	at
> org.apache.catalina.core.StandardWrapper.allocate(
> 	- locked <0x63a26708> (a java.util.Stack)
> 	at
> org.apache.catalina.core.StandardWrapperValve.invoke(
> 	at
> org.apache.catalina.core.StandardContextValve.invoke(
> And Bingo! we have found the problem.
> Now that stack trace might not ring alarm bells with someone unfamiliar
> with the Tomcat code base but if Tomcat is unresponsive, understanding
> why *any* thread is blocked would be a good place to start. If you look
> at line 854 and the surrounding code for StandardWrapper you will see
> that this is part of the Servlet allocation process. You should then
> realise that line 854 is part of Servlet allocation for Servlets that
> implement the SingleThreadModel (and now the alarm bells should be
> ringing loud and clear).
> Tomcat allocates a maximum of 20 instances of any STM servlet. Your
> client has an application that uses STM and requires many more than 20
> concurrent instances. Hence most requests are sat waiting for a STM
> instance to be released.
> Since that means there must be 20 instances of an STM Servlet already
> allocated, it is simple enough to grep the thread dump to find out which
> one. The winner is:
> com.motorola.nsm.common.ui.servlet.ValidateServlet
> Mark
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