Java Virtual Machine Performance Tuning

You can tune the Java Virtual Machine (JVM) settings to make a production system more efficient. 

You can configure the JVM parameters in the <ESB_HOME>/bin/wso2server.bat file (on Windows) or the <ESB_HOME>/bin/wso2server.sh file (on Linux/Solaris). Following are the most important JVM parameters you need to configure:

• Maximum Heap Memory Allocation (Xmx) - This parameter sets the maximum heap memory allocated for the JVM. Increasing the memory allocation increases the memory available for the ESB, which results in increasing the maximum TPS and reducing the latency. We recommend at least 2 GB of heap memory allocation for instances.
  For example, If you want to set 2 GB as the maximum heap memory size, you need to configure the parameter as follows:

  -Xms2048m -Xmx2048m -XX:MaxPermSize=1024m

  Here, 
  Xmx is the maximum memory allocation pool for a JVM.
  Xms is the initial memory allocation pool.
  XX:MaxPermSize is the permanent space where the classes, methods, internalized strings, and similar objects used by the VM are stored and never deallocated.

  When using JDK 1.8.*, you do not need to specify MaxPermSize since it has been removed with this version of Java.

• Metaspace size - In JDK 1.8.*, class metadata is stored in the native heap, and this space is called Metaspace. By default class metadata allocation is only limited by the amount of available native memory. If you need to limit the amount of native memory used for class metadata, you need to set MaxMetaspaceSize.
  To ensure stability of a production system, you can set the MaxMetaspaceSize parameter to 1GB as follows:

  -XX:MaxMetaspaceSize=1g

When an XML element has a large number of sub elements and the system tries to process all the sub elements, the system can become unstable due to a memory overhead. This is a security risk.

To avoid this issue, you can define a maximum level of entity substitutions that the XML parser allows in the system. You do this using the entity expansion limit as follows in the <ESB_HOME>/bin/wso2server.bat file (for Windows) or the <ESB_HOME>/bin/wso2server.sh file (for Linux/Solaris). The default entity expansion limit is 64000.

-DentityExpansionLimit=10000

In a clustered environment, the entity expansion limit has no dependency on the number of worker nodes.