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From Rainer Jung <tomcat-...@kippdata.de>
Subject Re: Any synchronization issues with SMP?
Date Wed, 23 Jun 2004 08:16:02 GMT
Hi,

we know one application running on 9 systems with 4 US II CPUs each
under Solaris 9. Peak request rates at 20 requests/second per system.
Tomcat is 4.1.29, Java is 1.3.1_09. No symptoms like yours!

You should send a signal "QUIT" to the jvm process during the
unresponsiveness time. This is a general JVM mechanism (at least for sun
JVMs). The signal writes a stack trace for each thread on STDOUT (so you
should also start tomcat with redirection of STDOUT the output to some
file). Beware: older JVM in rare cases stopped working after getting
this signal (not expected with 1.3.1_09).

In this stack dump you should be able to figure out, in which methods
most of your threads stay and what the status is.

Is there native code included (via JNI)? Any synchronization done in the
application itself? Are you using Tomcat clustering? Which JVM?

Sincerely

Rainer Jung

Martin Schulz wrote:

> Can someone confirm that Tomcat works well on busy SMP systems (e.g. Sun 
> V1280),
> or whether there are problems in Tomcat.
> 
> Here's what we have at our end:
> 
> We are currently performance testing our application (Tomcat 4.1.30) on 
> Solaris 9,
> on a V1280 system w. 8 CPUs. (SDK 1.4.2_04).  Transaction rates are 
> moderate, around 30/s.
> 
> The application, after about 30-40 minutes, gets unresponsive for a 
> little while (1-10 minutes),
> gets back to work (for a varying period of time, but definitely under 30 
> min), and then the cycle
> repeats.  At half the transaction rate, the smptoms are no longer easily 
> observed,.
> 
> The above symptoms disappear when we use a single CPU, or a single board 
> of 4 CPUs.
> That scenario seems to imply synchronization problems soemwhere in the 
> Java code.
> The problem could not be observed in development configurations either 
> (Wintel, 1-CPU Sun
> boxes.)
> 
> The behavior is such that connections get accepted, but no response is 
> sent (established connections
> remain at a fixed level).   The number of connections in this state 
> varies (20-70).
> 
>  From the timers we keep we learn that the service gets stuck when 
> reading the input.
> Once unblocked the responses get sent out rapidly again.
> 
> We have tuned the system for efficient, high-volume TCP-IP traffic.
> 
> We tried the coyote connector and the HttpConnector, both with the same 
> effect.
> 
> Please respond if you can confirm or dismiss threading issues in Tomcat.
> We would also be ineterested in testing approaches for such a scenario.
> 
> .I have kept system statistics for both scenarios and can provide these 
> on request.
> 
> Thanks!
>    Martin Schulz
> 
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