HTTP Compression of the Fortune 1000

Sept. 23, 2010 - PRLog -- HTTP compression, otherwise known as content encoding, is a publicly defined way to compress textual content transferred from web servers to browsers. HTTP compression uses public domain compression algorithms, like gzip and compress, to compress XHTML, JavaScript, CSS, and other text files at the server. This standards-based method of delivering compressed content is built into HTTP 1.1, and most modern browsers that support HTTP 1.1 support ZLIB inflation of deflated documents. In other words, they can decompress compressed files automatically, which saves time and bandwidth.

Stephen Pierzchala, Senior Technical Performance Analyst with Gomez, said this about HTTP compression:

"When tied to other methods, such as proper caching configurations and the use of persistent connections, HTTP compression can greatly improve Web performance. In most cases, the total cost of ownership of implementing HTTP compression (which for users of some Web platforms is nothing!) is extremely low, and it will pay for itself in reduced bandwidth usage and improved customer satisfaction."

Fortune 1000 Website Compression Statistics

Despite all of the advantages of HTTP compression on web performance (lower bandwidth bills, faster response times, higher conversion rates) the Fortune 1000 companies have lagged in adopting this standards-based technology. As of February 2010, only 26.7% of the top 1000 companies use HTTP compression on their websites (see Figure 1). Fully 73.3% of the top 1000 websites do not use HTTP compression on their sites, according to a recent survey by Pint, Inc.

The Browser / Server Conversation

Browsers and servers have brief conversations over what they'd like to receive and send. Using HTTP headers, they zip messages back and forth over the ether with their content shopping lists. A compression-aware browser tells servers it would prefer to receive encoded content with a message in the HTTP header like this:

GET / HTTP/1.1
Host: www.webcompression.org
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.5)
 Gecko/20031007 Firebird/0.7
Accept: text/xml,application/xml,application/xhtml+xml,text/html;q=0.9,
 text/plain;q=0.8,video/x-mng,image/png,image/jpeg,image/gif;q=0.2,*/*;q=0.1
Accept-Language: en-us,en;q=0.5
Accept-Encoding: gzip,deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive: 300
Connection: keep-aliveAn HTTP 1.1-compliant server would then deliver the requested document with using an encoding accepted by the client. Here's a sample response from WebCompression.org:

HTTP/1.1 200 OK
Date: Thu, 04 Dec 2003 16:15:12 GMT
Server: Apache/2.0
Vary: Accept-Encoding
Content-Encoding: gzip
Cache-Control: max-age=300
Expires: Thu, 04 Dec 2003 16:20:12 GMT
X-Guru: basic-knowledge=0, general-knowledge=0.2, complete-omnipotence=0.99
Content-Length: 1533
Content-Type: text/html; charset=ISO-8859-1Now the client knows that the server supports gzip content encoding, and it also knows the size of the file (content-length). The client downloads the compressed file, decompresses it, and displays the page. At least, that is the way it is supposed to work.

Browsers Can Lie

Unfortunately, some early versions of Netscape 4 say they support ZLIB inflation when they really can't. Rather than rely on the content negotiation built into Apache and IIS, most webmasters install software specifically designed to make this conversation an amicable one. Products like mod_gzip, Vigos' Website Accelerator, PipeBoost, httpZip, and others offer configurable compression that can avoid browser quirks.

Average Compression Ratios

So what can you expect to save using HTTP compression? In tests that we ran on twenty popular sites we found that on average, content encoding saved 75% off of text files (HTML, CSS, and JavaScript) and 37% overall.1 A similar study of 9,281 HTML pages of popular sites by Destounis et. al found a mean compression gain of 75.2%.2 On average, web compression reduced the text files tested to one-fourth of their original size.3 The more text-based content you have, the higher the savings.

Joe Lima, COO and Head of Product Development at Port80 Software, said this about HTTP compression:

"HTTP compression provides such a clear benefit that it appeals to all kinds of users. Our customers include consumer sites that want to improve end-users' experience, hosting providers seeking to differentiate their offering, Fortune 500's looking to make a specific extranet application as bandwidth-efficient as possible, and many others. Simply put, compression is easy to deploy, widely supported, and saves money. Who could say no to that?"

File Size Savings for Sites Using HTTP Compression

Here are three examples from popular sites that use HTTP compression. Google and Orbitz both use gzip compression to deliver compressed versions of their pages to HTTP 1.1-compliant browsers. Table 1 shows the size of their home pages plus one search results page before and after compression.

See HTTP Compression of the Fortune 1000 http://www.websiteoptimization.com/speed/tweak/compress/

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