Web Server Software Architectures

h thread of any process handling one request at a time (see Figure 1c). The Apache 2.0 Worker MPM implements an example of this type of approach (see http://httpd. apache.org/docs-2.0/mod/worker.html). One advantage of a process-based architecture is stability. The crash of any process generally does not affect the others, so the Web server continues to operate and serve other requests even when one of its processes must be killed and restarted. The architecture's drawbacks relate to performance: creating and killing processes overloads the Web server, mainly because of address-space management operations. Moreover, high-volume Web sites require many processes, which leads to non-negligible memory requirements and increased contextswitching overhead (see http://httpd.apache.org/ docs/misc/perf-tuning.html#preforking). A thread-based architecture is not as stable as a process-based one. A single malfunctioning thread can bring the entire Web server down because all threads share the