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My web site is gaining popularity quickly, but I can't afford to upgrade my hardware. What can I do to optimize Apache?
With the explosion of Internet use and its attendant traffic, keeping pace with rising demand is a common problem. Luckily, there are some concrete steps you can take to relieve system stress.
As with all performance problems, your first action should be to identify and ease bottlenecks. Use tools such as top, vmstat, and iostat to diagnose your system. Also, consider what kinds of content you are serving: if you use CGI, scripting, databases, or other tools to generate and serve dynamic content, analyze and optimize each of those subsystems, too.
Focus next on hardware. Lots of RAM is essential for smooth Apache performance -- you must have enough memory to avoid hitting swap. If you serve static content, raw CPU power shouldn't be a concern. However, if you serve dynamic content, the more processing power, the better. Also, make sure you have fairly fast disks, and, of course, enough network bandwidth.
There are also many ways to improve Apache's own performance. In Apache's configuration file, httpd.conf, it's important that you disable HostnameLookups. If left on, Apache waits for a DNS response before completing each and every request. (If you want to use reverse lookups to collect statistics, you can easily derive them after the log's been rotated. In fact, many log analysis programs even have this built-in.)
Whenever possible, enable FollowSymLinks and disable SymLinksIfOwnerMatch. This combination of settings avoids extra system calls for every request. Also, consider disabling the AllowOverride option. While .htaccess files are extremely convenient in mass hosting environments, all of its features are readily set in httpd.conf, and disabling it saves Apache from having to check for the files existence on every request.
You should also disable any unused Apache modules, which decreases the amount of memory that Apache uses. If an Apache module is built as a DSO, you can easily disable it by commenting out the module in httpd.conf and restarting Apache. However, if the module is compiled into Apache, you'll need to recompile Apache to remove the module.
If you're using Apache 1.3.x to serve a high-traffic web site using mod_perl or PHP, you can significantly improve performance by using lingerd. lingerd is a daemon designed to do nothing but properly close network connections from an HTTP server. Why is it needed? Due to the way TCP/IP works, Apache often spends a large amount of time doing a lingering_ close() for each connection. Using lingerd to handle this task allows Apache to handle more connections. Licensed under an Apache-style license, lingerd is available from http://www.iagora.com/about/software/lingerd.
Installing lingerd is straightforward, but it does require patching Apache (which, incidentally, is how the "a-patchy" server got its name). Assuming your Apache sources are in $APACHE, and you've unpacked the lingerd source tar file, do the following: