Detecting Timed-Out Client Requests for Avoiding Livelock and Improving Web Server Performance

A Web server’s listen queue capacity is often set to a large value to accommodate bursts of traffic and to accept as many client requests as possible. We show that, under certain overload conditions, this results in a significant loss of server performance due to the processing of so-called “dead requests”: timed-out client requests whose associated connection has been closed from the client side. In some pathological cases, these overload conditions can lead to server livelock, where the server is busily processing only dead requests and is not doing any useful work. We propose a method of detecting these dead requests and avoiding unnecessary overhead related to their processing. This provides a predictable and controllable platform for web applications, thus improving their overall performance. DTOC strategy is implemented as a part of WebQoS product for HP9000 servers [HP-WebQoS].