puting Practices journal, special issue on Distributed Object-

Oriented Systems, edited by Maria Cobb, 1999. This paper provides two contributions to the study of high-performance object-oriented (OO) Web servers. First, it out-lines the design principles and optimizations necessary to de-velop efficient and scalable Web servers and illustrates how we have applied these principles and optimizations to cre-ate JAWS. JAWS is a high-performance Web server that is de-signed to alleviate overheads incurred by existing Web servers on high-speed networks. In addition to its highly extensi-ble OO design, it is also highly efficient, consistently outper-forming existing Web servers, such as Apache, Java Server, PHTTPD, Zeus, and Netscape Enterprise, over 155 Mbps ATM networks on UNIX platforms. Second, this paper describes how we have customized the JAWS OO design to leverage advanced features of Windows NT on multi-processor platforms linked by high-speed ATM networks. The Windows NT features used in JAWS include asynchronous mechanisms for connection establishment and data transfer. Our previous benchmarking studies demonstrate that once the overhead of disk I/O is reduced to a negligible constant factor (e.g., via memory caches), the primary deter-minants of Web server performance are its concurrency and event dispatching strategies. Our performance results over a 155 Mbps ATM network in-dicate that certain Windows NT asynchronous I/O mechanisms (i.e., TransmitFile) provide superior performance for large file transfers compared with conventional synchronous multi-threaded servers. Conversely, synchronous event dis-patching performed better for files less than 50 Kbytes. Thus, to provide optimal performance, a Web server design should This work was supported in part by grants from OTI, Kodak, and Siemens. be adaptive, i.e., choosing to use different mechanisms (such as TransmitFile) to handle requests for large files, while using alternative I/O mechanisms (such as synchronous event dispatching) on requests for small files.