Administration guide > Tune and performance > Use WebSphere Real Time

WebSphere Real Time in WebSphere Application Server

Use WebSphere Real Time with eXtreme Scale in a WebSphere Application Server Network Deployment environment version 7.0. By enabling WebSphere Real Time, you can get more predictable garbage collection along with a stable, consistent response time and throughput of transactions.


Use WebSphere eXtreme Scale with WebSphere Real Time increases consistency and predictability at a cost of performance throughput in comparison to the default garbage collection policy employed in the standard IBM Java™ SE Runtime Environment (JRE). The cost versus benefit proposition can vary based on several criteria. The following are some of the major criteria:

In addition to this metronome garbage collection policy available in WebSphere Real Time, there are optional garbage collection policies available in standard IBM Java™ SE Runtime Environment (JRE). These policies, optthruput (default), gencon, optavgpause and subpool are specifically designed to solve differing application requirements and environments. For more information on these policies, see JVM tuning for WebSphere eXtreme Scale. Depending upon application and environment requirements, resources and restrictions, prototyping one or more of these garbage collection policies can ensure that you meet the requirements and determine an optimal policy.

Capabilities with WebSphere Application Server Network Deployment

  1. The following are some supported versions.

    • WebSphere Application Server Network Deployment version and above.

    • WebSphere Real Time V2 SR2 for Linux and above. See IBM WebSphere Real Time V2 for Linux for more information.

    • WebSphere eXtreme Scale version and above.

    • Linux 32 and 64 bit operating systems.

  2. WebSphere eXtreme Scale servers cannot be collocated with a WAS DMgr.

  3. Real Time does not support DMgr.

  4. Real Time does not support WebSphere Node Agents.

Enable WebSphere Real Time

Install WebSphere Real Time and WebSphere eXtreme Scale onto the computers on which you plan to run eXtreme Scale. Update the WebSphere Real Time Java to SR2.

You can specify the JVM settings for each server through the WAS version 7.0 console as follows.

Choose Servers > Server types > WebSphere application servers > <required installed server>

On the resulting page, choose "Process definition."

On the next page, click Java Virtual Machine at the top of the column on the right. (Here you can set heap sizes, garbage collection and other flags for each server.)

Set the following flags in the "Generic JVM arguments" field:

-Xrealtime -Xgcpolicy:metronome  -Xnocompressedrefs -Xgc:targetUtilization=80

Apply and save changes.

To use Real Time in WAS 7.0 to with eXtreme Scale servers including the JVM flags above, create a JAVA_HOME environment variable.

Set JAVA_HOME as follows.

  1. Expand "Environment".

  2. Select "WebSphere variables".

  3. Ensure that "All scopes" is checked under “Show scope".

  4. Select the required server from the drop-down list. (Do not select DMgr or node agent servers.)

  5. If the JAVA_HOME environment variable is not listed, select "New," and specify JAVA_HOME for the variable name. In the "Value" field, enter the fully qualified path name to Real Time.

  6. Apply and then save the changes.

Best practices

For a set of best practices see the best practices section in Use WebSphere Real Time. There are some important modifications to note in this list of best practices for a stand-alone WebSphere eXtreme Scale environment when deploying into a WAS ND environment.

You must place any additional JVM command line parameters in the same location as the garbage collection policy parameters specified in the previous section.

An acceptable initial target for sustained processor loads is 50% with short duration peek loads hitting up to 75%. Beyond this, add additional capacity before you see measurable degradation in predictability and consistency. You can increase performance slightly if you can tolerate longer response times. Exceeding an 80% threshold often leads to significant degradation in consistency and predictability.

Parent topic:

Use WebSphere Real Time

Related concepts

WebSphere Real Time in a stand-alone environment