In the drools documentation for "Using Rules at Runtime" it states - A RuleBase may be a managed object which is deployed by an administrator within a JNDI directory. This method of deployment allows an application to be isolated from changes in the rules. The rules can be easily altered and redeployed, enabling an on-the-fly modification of the behaviour of an application (etc). However, in the semantic java module, there are a number of classes which contains the transient fields: JavaCondition JavaBlockConsequence JavaFunctions PythonInterp This means whenever a rulebase is bound to JNDI tree, these java conditions and block consequences need to be reconstructed whenever a rulebase is looked up or materialized from JNDI, triggering a janino compile call. Under high load, the majority of time is spent in the janino compile method whereas if the JavaCondition / JavaBlockConsequence was declared nontransient, the compilation step can be skipped, improving performance under load.