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Figure 2: Multi-Process - In the MP model, each server process handles one request at a time. Processes execute the processing stages sequentially.

In the multi-process (MP) architecture, a process is assigned to execute the basic steps associated with serving a client request sequentially. The process performs all the steps related to one HTTP request before it accepts a new request. Since multiple processes are employed (typically 20-200), many HTTP requests can be served concurrently. Overlapping of disk activity, CPU processing and network connectivity occurs naturally, because the operating system switches to a runnable process whenever the currently active process blocks.

Since each process has its own private address space, no synchronization is necessary to handle the processing of different HTTP requests2. However, it may be more difficult to perform optimizations in this architecture that rely on global information, such as a shared cache of valid URLs. Figure 2 illustrates the MP architecture.

Peter Druschel