Chapter 10. Performance tuning considerations with the decision engine

The following key concepts or suggested practices can help you optimize decision engine performance. These concepts are summarized in this section as a convenience and are explained in more detail in the cross-referenced documentation, where applicable. This section will expand or change as needed with new releases of Red Hat Process Automation Manager.

Use sequential mode for stateless KIE sessions that do not require important decision engine updates

Sequential mode is an advanced rule base configuration in the decision engine that enables the decision engine to evaluate rules one time in the order that they are listed in the decision engine agenda without regard to changes in the working memory. As a result, rule execution may be faster in sequential mode, but important updates may not be applied to your rules. Sequential mode applies to stateless KIE sessions only.

To enable sequential mode, set the system property drools.sequential to true.

For more information about sequential mode or other options for enabling it, see Section 5.3, “Sequential mode in Phreak”.

Use simple operations with event listeners

Limit the number of event listeners and the type of operations they perform. Use event listeners for simple operations, such as debug logging and setting properties. Complicated operations, such as network calls, in listeners can impede rule execution. After you finish working with a KIE session, remove the attached event listeners so that the session can be cleaned, as shown in the following example:

Example event listener removed after use

Listener listener = ...;
StatelessKnowledgeSession ksession = createSession();
try {
} finally {
    if (session != null) {

For information about built-in event listeners and debug logging in the decision engine, see Chapter 8, Decision engine event listeners and debug logging.