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Web Performance Tuning by Patrick Killelea

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Configurable OS Parameters

Here, we go over optimum parameters for web services. Note that Unix systems are shipped with a generic kernel, optimized not for any particular use, but for acceptable performance for general use. See Chapter 10 for information on configuring TCP. You can see the current settings in a Solaris system by viewing /etc/system or grepping for “ndd” from inetinit. In general, Solaris 2.6 is already tuned for web services, so you shouldn’t have to modify anything to get the best performance. Here are a few of the most basic parameters you may want to tune on Linux or another OS. Remember to back up your kernel and configuration files before changing anything:

Number of file descriptors

File descriptors are positive integers by which the kernel keeps track of open files and network connections per process. If your web server software has a very large number of open files and connections in a process, it is possible to run out of file descriptors, meaning that you will not be able to accept new connections until old connections terminate and give up their descriptors. In programmer’s terms, the accept() system call will fail. What happens after that depends on your version of Unix; it may log an error to the system log or print a message on the console, among other things. Old versions of Unix had a file descriptor limit of 20 (as OPEN_MAX in limits.h for SVR4), but every system has increased it far beyond that. It is not unreasonable to want several thousand ...

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