compression and compressionMinSize in GlassFish v3

Friday Sep 26, 2008

In Enabling HTTP Compression in GlassFish, Jean-Francois discussed about compression in GlassFish. There are four properties to configure compression, namely:

• compression
• compressionMinSize (in OCTET)
• compressableMimeType
• noCompressionUserAgents

One can turn compression on and off by setting compression = force and compression = off respectively. And one can also turn on the compression if the content-length is unknown or known to be greater than a certain size. There are two properties related to this: compression and compressionMinSize. In this blog, we will discuss various ways to accomplish this scenario in GlassFish v3.

compression vs compressionMinSize

property	possible value if set	Default
compression	on, force, off, integer	off
compressionMinSize	integer	2048

There are several possible combinations. We will summarize the behaviors of GlassFish v3 in the below table. In the following, α and β are integers.

compression	compressionMinSize	Result
on	β	compression with min size β
on	not set	compression with default min size (2048)
force	β or not set	compression with no size constraint
α	β or not set	compression with min size α
off or not set	β or not set	no compression

So, roughly speaking, whenever there is conflicting information between compression and compressionMinSize, the compression property will take precedence.

Since we use strict inequality to check for known content length, the following are equivalent:

• compression = force
• compression = on and compressionMinSize = any negative integer

How to test it?

If one has turned on compression in GlassFish, then one will get HTTP compression if the HTTP request is

• using HTTP 1.1
• with a HTTP header:
      Accept-Encoding: gzip
• the content-length is unknown or greater than the compression minimum size
  (or compression = force)

One can confirm that there is a HTTP compression by using Firefox with Firebug. There will be a HTTP response header:

• Content-Encoding: gzip

Note that one can also notice some changes in HTTP response for HTTP compression by using the http client posted in one of my previous blogs.