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.
View the original post :
Reply to the post :