Web Performance Tuning

Runtime Configuration Issues

HostnameLookups

Prior to Apache 1.3, HostnameLookups defaulted to On. This adds latency to every request, because it requires a DNS lookup to complete before the request is finished. In Apache 1.3, this setting defaults to Off. However (1.3 or later), if you use any allow from domain or deny from domain directives, then you will pay for a double reverse DNS lookup (a reverse, followed by a forward to make sure that the reverse is not being spoofed). So for the highest performance, avoid using these directives (it’s fine to use IP addresses rather than domain names).

Note that it’s possible to scope the directives, such as within a <Location /server-status> section. In this case, the DNS lookups are only performed on requests matching the criteria. Here’s an example which disables lookups except for .html and .cgi files:

HostnameLookups off
<Files ~ "\.(html|cgi)$>
    HostnameLookups on
</Files>

Still, if you just need DNS names in some CGIs, you could consider doing the gethostbyname call in the specific CGIs that need it.

FollowSymLinks and SymLinksIfOwnerMatch

Wherever in your URL-space you do not have an Options FollowSymLinks , or you do have an Options SymLinksIfOwnerMatch , Apache will have to issue extra system calls to check up on symlinks—one extra call per filename component. For example, if you had:

DocumentRoot /www/htdocs
<Directory />
    Options SymLinksIfOwnerMatch
</Directory>

and a request is made for the URI /index.html, then Apache will perform ...