[jboss-user] [JBoss jBPM] - Re: jBPM BPEL: Process Performance and Workload ?

alex.guizar@jboss.com do-not-reply at jboss.com
Mon Oct 9 15:33:16 EDT 2006

1) Well, as you know, endpoints backed by a BPEL process are stateful. In general, you will have a process instance per request, unless two or more requests correlate to the same process instance. In this case these requests will execute the same instance.

This is a consequence of the design of the BPEL language. You can expect performance similar to stateful session beans in the EJB domain.

2) In jBPM, a process instance is composed of one or more tokens. Each token represents a path of execution. Initially, a process instance contains a single token which represents the main path. When the process logic encounters an activity with more than one path of execution (the flow activity, a scope with event handlers, etc) the engine spaws one token per path.

jBPM runs these paths serially to avoid starting new threads because this is forbidden in a Java EE environment. This might look bad, but in practice it is not: jBPM stops executing a path of execution when it encounters a blocking activity (these include inbound message and time-driven activities). 

When jBPM stops executing a path, a separate server thread must resume the execution of that path. This is where JMS  is critical to the BPEL runtime: it allows for executing more than one path of the same process instance in parallel, while fully adhering to Java EE guidelines.

To illustrate, consider the following example:
  |  <receive name="a" createInstance="yes"/>
  |  <flow>
  |   <sequence name="b">
  |    <invoke name="b1"/>
  |    <receive name="b2"/>
  |   </sequence>
  |   <sequence name="c">
  |    <assign name="c1 />   
  |    <receive name="c2" />
  |   </sequence>
  |  </flow>
  |  <reply name="d"/>
  | </sequence>
The order of execution is:
a, b1, c1
c2, d

Note that d executes in either thread-2 or thread-3 depending on what request arrives first, b2 or c2

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