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From János Löbb <>
Subject Re: Tomcat not using multiple cores
Date Fri, 17 Oct 2008 13:53:28 GMT

On Oct 16, 2008, at 9:05 PM, Matthew Laird wrote:

> Caldarale, Charles R wrote:
>> "The only time I began to see the other cores actually start being  
>> used is when I enabled multi-threaded GC.  But that doesn't give  
>> much improvement since the threads responding the web requests are  
>> still all on the same core."
>> The most likely cause is internal synchronization in the webapp or  
>> the database it references.
> I've heard similar from someone else but I'm not sure how that's  
> possible.  The app is not at all threaded, is 100% read-only from  
> the database (aside from creation of temp tables which have no  
> interaction between client requests) and the MySQL server is on  
> another machine humming along without any bottlenecks that I can see.
> But of course I'm not a Java or JVM expert and have no idea what  
> kind of interlinks can exist between different client connections.   
> But to my knowledge they're all pretty straight forward handlers,  
> "get data from database, format, return to user"
> I'm leaning more towards GC issues.  I setup Tomcat on a 64-bit  
> machine and tried a few configurations:
> -Xms4096M -Xmx4096M -server -XX:+DisableExplicitGC -XX: 
> +UseConcMarkSweepGC
> -Xms4096M -Xmx4096M -server
> -Xms2048M -Xmx2048M -server
> As I went through each of those the app became more and more  
> sluggish and a single core finally in the last configuration did  
> this 100% CPU usage again.
> Now, two issues I see.  First, it's not being aggressive enough at  
> spreading the load among different cores.  Second, GC does seem to  
> be an issue.
> Unless I'm missing something, which I might be.
> Thanks.

Make sure IP6 is not enabled if You are an IP4 network.  We had  
problems like You describe because of it.

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