RE: Optimizing for Java and Tomcat (x-posted)

"Optimize" is a loaded term. I don't know of any methods to optimize, though I know a few tricks to make java (and Tomcat) run faster.

First, run java in its own storage pool. There's a couple ways to do this. I create a separate subsystem and allocate a pool to it. I allocate either a private pool or one of the *SHRPOOLxx's. I make the pool big enough to handle the size I specify as Xmx in the java command. Java allocates memory very quickly and then doesn't refer to it for a long time, so it tends to page out. That leads to a lot of page faults when the garbage collector runs or when your application goes back to an instance object or a class object it hasn't used in a while. Making the memory pool big enough mitigates this problem. You could also use routing entries in a shared subsystem to route the java jobs to a certain memory pool.

The J9 jvm's beat hell of the classic except in rare circumstances. On older versions of the OS, that's usually what's known as the "32 bit" jvm. On newer systems, there's 64-bit versions of some J9's depending on Java version. The 64-bits take more room (memory) but if you have the memory, they really smoke. If you don't have memory to spare, use the 32-bit as the page faults will drop and that makes up for and loss in speed.

Optimization would require methods for changing some of these parameters, running a repeatable load through each set, and comparing the time spent. It'd be a great tool, but I don't know that it exists.

-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx [mailto:midrange-l-
bounces@xxxxxxxxxxxx] On Behalf Of DeLong, Eric
Sent: Wednesday, November 20, 2013 4:47 PM
To: Midrange Systems Technical Discussion
Subject: RE: Optimizing for Java and Tomcat (x-posted)

Choose a better JVM? We still use classic jvm here, but we're looking at 32
bit jvm for better performance. The selection of jvm depends a great deal
on the nature of the application, but in general, I believe 32 bit jvm will
perform better on a typical IBM i for typical Java applications...

JMO,
-Eric DeLong

-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx [mailto:midrange-l-
bounces@xxxxxxxxxxxx] On Behalf Of James H. H. Lampert
Sent: Monday, November 18, 2013 6:12 PM
To: Midrange Systems Technical Discussion; Java 400 List
Subject: Optimizing for Java and Tomcat (x-posted)

What can be done to optimize the running of Java applications in
general, and Tomcat in particular, on current midrange boxes?

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JHHL
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