2009/10/5 prashant sharma :
> Tomcat: 5.0.
That's old, and no longer supported. Why are you using this version?
(And exactly which version of 5.0 are you using, by the way?)
> OS: Windows Server HPC edition.
32- or 64-bit? I ask because the maximum contiguous memory you'll get
in 32-bit is somewhere around 1400 Mbytes - the numbers vary depending
on exactly which Microsoft OS.
> JVM: 5.0
That's also old. Why are you using this version?
> There is one basic doubt that I have. When we load/stress our Tomcat server,
> we hit thresholds mentioned below once in a while. The root of the problem is
> that when I increase the clients, I start getting a connection refused error
> on the server side. This is because the server hits the maximum request
> processing thread limit. The other problems are connected to it:
>
> -Max threads (tomcat):
>
> As mentioned above, this is the root of the problem. To solve this problem, I
> increase the max threads in server.xml. Then I get the Out of stack space
> exception.
>
> -Stack Memory:
>
> Now for this I tried a couple of things
> a) Reduce the stack size allotted per thread so that more threads can be
> spawned in the allotted stack space.I believe that the default is around
> 320K/ thread. I set it to 128K in the JVM options (Xss).
> b) Reduce the heap size. I did this because as per my understanding the
> memory alloted to a process is divided among heap and stack. So probably
> reducing the heap size makes more memory available for stack. Don't know if
> this is correct?
It certainly makes more memory available for the OS stack.
> Now once in a while I get Out of memory exception for heap space.
>
> -Heap Memory:
>
> Can somebody advise as to what are the solutions for these sort of problems
> other than reducing the memory/thread consumption, of our application logic.
> I mean are there techniques that can be applied on tomcat/JVM/OS level to
> make more threads/memory available to the tomcat process?
OS: Use a 64-bit OS. Add RAM to the server. Use anything other than
32-bit Windows in order to get a larger contiguous heap space. If you
absolutely have to use Windows, and it absolutely has to be the 32-bit
version, use the /3GB switch *with extreme care* - read up on
*exactly* what it does and what will break before enabling it.
JVM: You've done the main thing, which is to reduce the stack depth per thread.
Tomcat: Memory and CPU usage is generally better in newer versions.
Other tunings are very much application-specific, I suspect.
However, I think we all know what the underlying problem is: your
application will not reliably fit in the available space with the load
you're putting on it during the test. Add more space, load-balance
onto multiple machines of the size you have, tune the app, or reduce
the scale of your load test if it's deliberately a long way above your
target load.
- Peter
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