WSO2 ESB is one of the fastest enterprise service bus solutions around. It's lightweight, doesn't eat up too much memory and CPU, and capable of handling thousands of concurrent requests with only a handful of worker threads. An out of the box WSO2 ESB installation configured for a pass through scenario, can provide a throughput close to 6000 transactions per second on average.
And it gets better. WSO2 ESB comes with a couple of performance optimizers that can be used to get an even higher throughput from the ESB. Recently we did a performance benchmark between these different performance optimizers and the mint WSO2 ESB. We have now published the results of these tests at our website. According to the results, the pass through HTTP transport, our latest performance optimizer, provides the highest throughput. With 2000 concurrent connections sending 1K sized messages, the pass through transport could provide a throughput of 18000 transactions per second.
One of the limitations in these performance optimizers is that they restrict the type of scenarios that you can run on the ESB. For instance the pass through transport currently can only support pass through proxy scenarios. It cannot be used with transformation or any other type of payload manipulation use cases. We are currently working on making the pass through transport capable of dealing with such content aware scenarios as well. In fact we want the ESB to run with the pass through transport by default for all scenarios.