A frequent criticism of XML-based Web services is that they tend to perform poorly under heavy load. While performance was a sore spot of early Web service implementations, performance-related investments in more recent Web service tools seem to have paid off, according Bharath Mundlapudi in a recent Sun Developer Network article, Implementing High-Performance Web Services Using JAX-WS 2.0. Although XML processing is still a dominant aspect of Web services performance, Mundlapudi shows that Web service performance is a result of the interaction of several components:

You can measure the performance of the web services stack in two ways, depending on your deployment model: end-to-end performance and endpoint performance... If a web service deployment involves [both] the client and server stack[s], then measurements in the performance tests should include both of these components [in end-to-end testing]... [In endpoint performance testing,] the only concern is the endpoint, that is, the server-side performance.

Mundlapudi offers a few guidelines to obtain the best performance from a Java Web service:

• Choose the primitives depending on the requirements —such as the number of digits, precision, and so on—because primitives can affect the performance based on their usage.
• An increase in payload size will reduce the throughput and have considerable effect on performance.
• JAXB binding or schema binding provides better performance than does DOM or nonschema binding.
• JAX-WS 2.0 gives better binding performance than does JAX-RPC 1.1.
• For large payload sizes, the performance of JAX-WS 2.0 is about twice that of JAX-RPC 1.1.

A key point in Mundlapudi's article is that Web service performance depends only in part on SOAP performance, and that, in fact, a large part of Web service performance relates to binding Java data types to XML and vice versa. Even without using SOAP, a REST or HTTP-based Web service that uses data binding will have to incur that overhead.

What's your experience with the performance of Java-based Web services, SOAP-based or otherwise?