There are several parameters in httpd.conf file that I pay attention to. Although the default values normally work out for me, sometimes they need to be tweaked for better performance.
Apache can look up the visitor's ip and come up with the hostname. And this process will likely slow down the server a bit.
The max number of child process to spawn. Each Apache child process will take up some memory so this count should be determined on the available memory (total memory – allocation for other processes) and normal Apache child process size.
Whether to re-use the connection for multiple HTTP requests. Opening socket is an expensive process. The KeepAlive option can help reduce the overhead of frequent connections.
KeepAliveTimeout = 15
The number of seconds to keep a socket alive waiting on other request. Setting this number to high can cause the too many connections linger and evetually no more connections are available when the MaxClients is reached.
Disconnect when idle time reaches this value. Depending on the average page loading time it can be lowered to reduce the hanging request.
The size of the ouput buffer. Normally I don't mess with this setting as far as it's a reasonable value and big enough for most of my web page sizes.
Directory settings – The <Directory> tag for the web server root
AllowOverRide All – tells Apache to pick up the .htaccess setting from each individual directory if available. For better performance this needs to be set to none since Apache will attempt to open .htaccess for each file name request.
Options Index – tells Apache not to perform directory listing when there is no default pages like index.htm(l)…
Options FollowSymLinks - Apache sever will follow the symbolic links.
Options SymLinksIfOwnerMatch – do not set this.
Allow directive – If there is need to control which hosts can access the server, use the ip address as much as possible. For example, "Allow from 10.1.2.3" is better than "Allow from allowedhost.com". When the server sees a hostname, it will perform a reverse DNS lookup on the ip to get the hostname, and then do a forward lookup on the hostname to assure the ip addresses match. And this is an expensive process.
Only enable the necessary ones to keep the server lean and mean.