Understanding Compression

Regular text and most non-image content are well suited for compression. Text files can typically be compressed by 70% or more. Compression can save significant bandwidth and enable faster browser response times. The effect is negligible in most high speed LAN environments, but is quite noticeable for users on slow WAN connections.

Compression is not recommended for files that are already compressed. A partial list includes these types of files:

• zip

• PDF

• exe

• image files

Compressing these file types using mod_deflate can actually increase their size or corrupt the files.

There are 9 levels of compression available when using mod_deflate. The difference between the default level (6) and the maximum compression level (9) is minimal, and the cost in extra CPU time necessary to process the higher compression level is significant and ultimately not beneficial. For this reason, you should use the default compression level.