High Performance Web Sites

Configuration

The module used for configuring gzip depends on your version of Apache: Apache 1.3 uses mod_gzip while Apache 2.x uses mod_deflate. This section describes how to configure each module, and focuses on Apache because it is the most popular web server on the Internet.

Apache 1.3: mod_gzip

Gzip compression for Apache 1.3 is provided by the mod_gzip module. There are many mod_gzip configuration directives, and these are described on the mod_gzip web site (http://www.schroepl.net/projekte/mod_gzip). Here are the most commonly used directives:

mod_gzip_on

Enables mod_gzip.

mod_gzip_item_includemod_gzip_item_exclude

Define which requests to gzip or not to gzip based on file type, MIME type, user agent, etc.

Most web hosting services have mod_gzip turned on for text/html by default. The most important configuration change you should make is to explicitly compress scripts and stylesheets. You can do this using the following Apache 1.3 directives:

mod_gzip_item_include         file       \.js$
mod_gzip_item_include         mime      ^application/x-javascript$
mod_gzip_item_include         file       \.css$
mod_gzip_item_include         mime      ^text/css$

The gzip command-line utility offers an option that controls the degree of compression, trading off CPU usage for size reduction, but there is no configuration directive to control the compression level in mod_gzip. If the CPU load caused by streaming compression is an issue, consider caching the compressed responses, either on disk or in memory. Compressing your responses and updating ...