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From "Vadim Gritsenko" <vadim.gritse...@verizon.net>
Subject RE: Possible points of scalibility issues
Date Wed, 13 Feb 2002 20:37:15 GMT
A little bit on another (but connected) topic...

> From: Berin Loritsch [mailto:bloritsch@apache.org]
> 
> I have been performing some performance analysis of the Avalon 
> Excalibur code, and I discovered
> some serious points of thread contention.  In a web environment,
> there can be as many as 150
> threads (or more) if the web server uses simple thread per 
> connection technology
> (most common aproach for Java based servers like Tomcat). 
> I expanded the Profile tests to work
> using 100 threads.  The default pooling implementation has 
> some serious slowdown due to thread contention.

<snip summary="Avalon enhancements"/>
 
> In the interim, I would suggest limiting the number of threads that
your
> Servlet container will
> allow to be used on Cocoon to around 40--but when the core is made
better, we
> won't need to have those limitations.

I see one weak link in this: After you spend lots of time eliminating
synchronization bottlenecks (which is good!!!), you will get into
another issue: thread switching is actually done by the operating
system, and increasing number of threads will result in larger
performance penalties caused by thread switching in the operating
system. Next level will be the context switch in the CPU hardware which
is costly operation.

Better (IMHO) thing to do is to switch to the asynchronous I/O API and
to use limited number of worker threads, which should give better
performance then increasing number of threads. Am I correct here?

Vadim


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