Starting from SAP NetWeaver 7.1, the Java stack does not have a dispatcher node as it was the case with earlier release. The job of the dispatcher--load balancing the incoming HTTP requests to J2EE server nodes--is now taken over by ICM. The ICM is designed to load balance http sessions (stateful http calls), which is not optimal for applications like PI which primarily uses stateless calls. The result is decreased message throughput.
In order to optimize load balancing on SAP PI (7.1 to 7.3) add the parameters below in the SAP instance profile:
j2ee/HTTP/request_strategy = STATELESS
Restart ABAP+Java instances to activate these changes.