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Don,
Sorry for the late reply;
>I do not understand how the garbage collection would make the
>JVM CPU usage jump to 50%.
An application I have running atop of JServ uses approx a 17 meg stack and
the CPU breaths between 5% and 13% at most loads on a 500 Mhz single
processor machine. There was an article a few months ago at IBM/Alphaworks
on setting the JVM's max and minimum stack memory settings. If you set the
stack memory at 128 meg and your application only uses 20, the stack memory
will fill out until finally all the 108 meg not used by the app is GC'ed.
Alternatively if you set the stack memory at 16 Meg and your app uses 50
Meg, the JVM will be bogged down by continually sweeping for garbage to free
up the stack. You can set this in jserv.properties under
wrapper.bin.parameters. ie;
wrapper.bin.parameters=-Xms64m -Xmx64m
will set the JVM memory stack to be 64 Mb max and min.
>Could JServ trigger the JVM to jump like that.
>If so how? How could I monitor this to see what causes this.
I doubt it, I have never seen JServ do that on it's own. Have a look that
your application isnt suddenly generating several thousand classes and then
de-referencing them. Also have a look at how your db pool is setup, I have
noticed that when the db pool instantiates it asks for a bunch of resources.
If you are continually generating new db connections, try using a singleton
based connection pool. That will help as well.
>The logs have basically been useless. Do the JServ logs
>reflect any messages coming from the JVM?
Yes, but you have to tell JServ that you want to listen to that sort of
information first. You have to set the JVM settings in
wrapper.bin.parameters in jserv.properties. You can set the startup switches
for the JVM from here.
>Are there monitoring tools for NT to determine how this happens?
If you wish to have a look at how when the GC is being called by the JVM add
to your JServ config in jserv.properties;
wrapper.bin.parameters=-verbose:gc
IIRC it will appear in your jserv.log file. NT differs greatly between
JVM's, I would try out several differant JVM's on NT and settle on the most
stable, all of them from 1.2.1 onwards seem to be fast enough but stability
differs depending on the application running on top of them. Between 1.2.1
and 1.2.2 there was a change in how the prepared statement handled closing a
resultset with ODBC so watch out for that memory leak. I would also test the
JDK JVM's against the JRE JVM's. I dont know why but with NT the JDK JVM's
have appeared to be more robust but that is just my impression.
Cameron Riley
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