If you don't much care about logging in logs from which domain / hostnames requests to webserver originate and you want to boost up the Apache Webserver performance a bit especially on a heavy loaded Websites, where no need for stuff like Webalizer, Awstats etc. , e.g. you're using GoogleAnalytics to already track requests (beware as sometimes GoogleAnalytics could be missing requests to your webserver, so having some kind of LogAnalyzer software on server is always a plus). But anyways accepting that many of us already trust GoogleAnalytitcs.
Then a great tuning option to use in default domain configuration or in multiple VirtualHosts config is:
If you want to make the HostnameLookups off as a default behaviour to all your virtualhosts on Debian / Ubuntu / CentOS / SuSE / RHEL distro virtualhosts add either to default config /etc/apache2/sites-enabled/000-default (on Deb based Linuxes) or (on RPM based ones), add directive to /etc/httpd/httpd.conf
For self-hosted websites (if run your own small hosting) or for a home situated webservers with up to 20-50 websites it is also a useful optimization tip to include in /etc/hosts file all the IPs of sites with respective domain names following the normal syntax of /etc/hosts, e.g. in my own /etc/hosts, I have stuff like:
pcfreak:~$ cat /etc/hosts
127.0.0.1 localhost localhost.localdomain
127.0.1.1 pcfreak.www.pc-freak.net pcfreak mail.www.pc-freak.net
22.214.171.124 pcfreak.biz www.pc-freak.net www.pc-freak.net
# for wordpress plugins
# The following lines are desirable for IPv6 capable hosts
# … etc. put IPs and hostnames following above syntax
As you see from above commented section for wordpress plugins, I've included some common websites used by WordPress enabled plugins to prevent my own hosting server to query DNS server every time. The normal way the Linux / Unix works is it first checks in /etc/hosts and only if the hostname is not defined there then it queries the DNS caching server in my case this is a local DJBDNS cache server, however defining the hosts in /etc/hosts saves a lot of milisecons on every request and often if multiple hosts are defined could save (decrease site opening for end users) with seconds.
Well now use some website speed testing plugin like Yslow, Firebug Fiddler or HTTPWatch