When you call Oracle Support with a problem like apj12 errors in your mod_jserv.log, middle-tier Java Virtual Machines (JVMs) crashing, or poor middle-tier performance, then it will often be suggested to increase the number of JVM processes.  So, the key question that likely occurs to you is, “How many JVMs are required for my system?”

Processing Java Traffic in Groups

First, some quick background:  web requests received by Oracle HTTP Server (Apache) to process Java code is sent to one of four different types of JVM groups to be processed.   You can see this in the jserv.conf file:

ApJServGroup OACoreGroup 2 1 /usr/…/

ApJServGroup DiscoGroup  1 1 /usr/…/

ApJServGroup FormsGroup  1 1 /usr/…/

ApJServGroup XmlSvcsGrp  1 1 /usr/…/

The number of JVMs for each group is signified by the first number on each line.

OACoreGroup is the default group.  This is where most Java requests will be serviced

DiscoGroup is only used for Discoverer 4i requests

FormsGroup is only used for Forms Servlet requests

XmlSvcsGrp is for XML Gateway, Web Services, and SOAP requests

In the example above, I have two JVMs configured for OACoreGroup and one JVM configured for each of the other groups.

Factors Affecting Number of JVMs Required

Determining how many JVMs to configure is a complex approximation, as many factors need to be taken into account.  These include:

Hardware specification and current utilization levels

Operating system patches and kernel settings

JDK version and tuning

Applications code versions, especially JDBC and oJSP

JServ configuration file tuning ( and

Applications modules being used

How many active users

User behaviour

Rough Guidelines for JVMs

Luckily, Oracle Development have undertaken various performance tests to establish some rules of thumb that can be used to configure the initial number of JVMs for your system.


1 JVM per 100 active users


Use the capacity planning guide from Note 236124.1 “Oracle 9iAS Discoverer 4i: A Capacity Planning Guide”


1 JVM per 50 active forms users


1 JVM is generally sufficient

In addition to this, Oracle generally recommends no more than 2 JVMs per CPU.    You also need to confirm there are enough operating system resources (e.g. physical memory) to cope with any additional JVMs.

Your Mileage Will Vary

The general guidelines above are just that — they’re very broad estimates, and your mileage will vary.  As I write this, the Applications Technology Group is working on a JVM Sizing whitepaper that will provide guidelines based on whether your E-Business Suite deployment is small, medium, or large.  I’ll profile this whitepaper here as soon as it’s released publicly.

Until then, it’s critical that you test your environment under load, using transactional tests that closely mirror what your users will be doing.  It’s useful to use automated testing tools for this, as you create your benchmarks.

Nagulu Polagani

"We are all apprentices in a craft where no one ever becomes a master."

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