[jboss-user] [Performance Tuning] - Re: JBoss Community DOC-10217 - advice on tomcat connector t

PeterJ do-not-reply at jboss.com
Mon Dec 1 12:22:57 EST 2008

The problem with using recommendations is that often they are specific to the environment of the user. And sometimes the recommendations are not necessarily the best especially if the recommendation is based on a performance test. For example, one of the recommendations is for setting sun.rmi.dgc.client.gcInterval to 60 minutes. Why 60 minutes? Because the specjappserver performance test runs in under 60 minutes so the "recommended" setting prevents stray full GCs from being called during the test run.  But in a real life production environment, I would set it to once a day or once a week.

Having said that, the Tomcat documents, since they describe the settings in general terms, are better references on how the settings work.

(Examples below use the default values)

MinSpareThreads is the minimum number of unused threads that will be kept available to handle new incoming requests. Example: if 20 threads are actively in use, there will be at least 24 threads (20 in use + 4 spare).

A side effect is that this setting also dictates the initial number of threads created. Example: 0 threads in use, thus 4 threads. (I believe this is where the 'peak load' recommendation comes from - in a test such as specjappserver you can easily calculate the peak load and thus set minsparethreads to create that number of threads as part of system startup.)

At some point the system might get busy and you end up with, say. 200 threads. Then everyone goes to lunch and only 20 threads are busy. When the idle thread timeout is reached, the thread count will be reduced to 70 (20 active plus 50 spare).

Having said all of this, my testing has shown that Tomcat 6, and thus the versions of JBoss Web Server based on it, while it still accepts and stores these values no longer uses they to manage the threads. The min and max idle thread values are no longer checked in the source code (at least, it is no longer where it used to be checked and I haven't found any alternate locations where they are checked), and the observed behavior appears to validate the claim that they are no longer used.

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