Configuring and tuning the Java Virtual Machine (JVM)

The initial configuration of JVM settings for the Jazz applications is relatively straightforward. Start all deployments with the default settings, and adjust them only after serious consideration (which may include analysis). The details of this page are significantly out-of-date (post 3.x) and there are pages elsewhere with more appropriate recommendations. The theory listed here though is still valid and for now this page contains to have some merit, although this will be reviewed and updated.

General Guidance

In most Jazz implementations, CLM 2011 used the following settings:

-Xmx4G
-Xms4G
-Xmn512M
-Xgcpolicy:gencon
-Xcompressedrefs
-Xgc:preferredHeapBase=0x100000000

The garbage collection algorithm used above is referred to as gencon, and it will perform optimally for most situations. In some cases, with particular workloads, a modification of the garbage collection algorithm can be beneficial for performance. For a discussion of the various garbage collection algorithms and their impact on performance, read Garbage collection policies, Part 1 on the IBM developerWorks website.
.

|Note: When allocating memory to the JVM (or JVM’s) on a particular server, a good rule of thumb is that the amount of memory allocated to the JVM’s should be, at most, half of all of the available memory. The system also needs memory for operating system related activity and node agent (web server) operations. The settings shown here are a valid starting point for a system that has 8 GB of available memory.
CLM 6.x Sizing Advice explains a few other considerations that have emerged since the 3.x series.

The load on the system is determined by the workload, which is variable and depends on the users and the usage models. Planning your server needs based on concurrent user counts will not be accurate, but it is often the only measure that some organizations have available to them.

|Note: Rational Requirements Composer (until Rational DOORS NEXT Generation 5.0.1) must share a repository with the JTS. This does not mean that they need to reside on the same WebSphere Application Server instance. For versions prior to Rational Requirements Composer 4.0.1, an upper limit of 200 concurrent users per Rational Requirements Composer instance is a good rule of thumb. For Rational Requirements Composer 4.0.1 and beyond, an upper limit of 400 concurrent users per Rational Requirements Composer instance is a good rule of thumb. Another good rule of thumb is not to exceed 200 projects on a single Jazz application server.

Default settings

Hardware requirements

The server should be 64-bit and a minimum of 8 GB RAM.

Solaris

-Xmx4g -Xms4g -Xmn512m -XX:MaxPermSize=768M -XX:ReservedCodeCacheSize=512M -XX:CodeCacheMinimumFreeSpace=2M

AIX

-Xmx4g -Xms4g -Xmn512m -Xgcpolicy:gencon -Xnocompressedrefs

Linux

-Xmx4g -Xms4g -Xmn512m -Xgcpolicy:gencon -Xcompressedrefs -Xgc:preferredHeapBase=0x100000000

Windows

-Xmx4g -Xms4g -Xmn512m -Xgcpolicy:gencon -Xcompressedrefs -Xgc:preferredHeapBase=0x100000000

Notes

• WebSphere Application Server sometimes sets Xcompressedrefs automatically
• The -Xmx and -Xms settings should never equal or exceed the total amount of memory of the server
• In general we suggest the use of the gencon garbage collection algorithm in the JVM (-Xgcpolicy:gencon)
  • If more JVM memory is required, the suggestion is that the nursery setting should be one-eighth (1/8) of the start and max setting, as in:

-Xmx{N} -Xms{N} -Xmn{N/8}

Modifying settings

Where to find the settings in WebSphere (WebSphere Application Server)

These instructions are for WebSphere Application Server v8.x. For other versions of WebSphere Application Server, consult Setting generic JVM arguments in WebSphere Application Server

1. In the Administration Console select Servers
2. Expand Server Type and select WebSphere application servers
3. Click on the name of your server
4. Expand Java and Process Management and select Process Definition.
5. Under the Additional Properties section, click Java Virtual Machine.
6. Scroll down and locate the textbox for Generic JVM arguments.

Where to find the settings in Tomcat

When using the Tomcat application server, you should be able to just start up the Tomcat server. The default settings should work fine in most cases. You can adjust the settings used for the JVM by editing the server.startup file in the server directory under your JAZZ_HOME directory. The section with the JVM settings will look like this:

JAVA_OPTS="$JAVA_OPTS -Djava.awt.headless=true"
JAVA_OPTS="$JAVA_OPTS -DSQLSERVER_JDBC_DRIVER_FILE=$SQLSERVER_JDBC_DRIVER_FILE"
JAVA_OPTS="$JAVA_OPTS -DORACLE_JDBC_DRIVER_FILE=$ORACLE_JDBC_DRIVER_FILE"
JAVA_OPTS="$JAVA_OPTS -DDB2I_JDBC=$DB2I_ABSPATH"
JAVA_OPTS="$JAVA_OPTS -DDB2Z_JDBC=$DB2Z_ABSPATH"
JAVA_OPTS="$JAVA_OPTS -Dorg.eclipse.emf.ecore.plugin.EcorePlugin.doNotLoadResourcesPlugin=true"
JAVA_OPTS="$JAVA_OPTS -DJAZZ_HOME=file://"`pwd`"/conf"
JAVA_OPTS="$JAVA_OPTS -Dcom.ibm.team.repository.tempDir=$TEMP_DIR"
JAVA_OPTS="$JAVA_OPTS -Dlog4j.configuration=file://"`pwd`"/conf/startup_log4j.properties"
JAVA_OPTS="$JAVA_OPTS -Xmx1200M"
JAVA_OPTS="$JAVA_OPTS -Xms1200M"
JAVA_OPTS="$JAVA_OPTS -Xmn300M"

Be sure that you have considered the following things:

• Will you be configuring non-default (9080, 9443) port numbers for your Public URI?
• Will you be running Tomcat as a Windows service?
• Will you be using LDAP and configuring Tomcat to use the LDAPLocalGroup realm? You might also want to check out Configuring and tuning Lightweight Directory Access Protocol (LDAP).

Related topics: Configuring and tuning LDAP

External links:

• Setting generic JVM arguments in WebSphere Application Server
• JVM Garbage collection
• IBM developerWorks

Additional contributors: None