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Advanced Web Performance Optimization Chapter 9

Now that you've learned how to crunch your content, let's look at some more advanced server- and client-side techniques for increasing web performance.

On the server-side, this chapter explores methods that you can use to boost performance by:

  • Optimizing parallel downloads
  • Caching frequently used objects
  • Using HTTP compression
  • Deploying delta encoding
  • Rewriting URIs with mod_rewrite

On the client side we'll investigate procedures that you can use to improve the speed of content delivery including:

  • Delaying script loading
  • Progressive enhancement
  • Loading JavaScript on Demand (Remote Procedure Calls)
  • Inline Images with Data URIs

Although these techniques take some additional effort, they boost both perceived and actual web page speed. What follows is an outline of this chapter:

Further Reading

High Performance Web Sites: Essential Knowledge for Front-End Engineers
After you've tried everything else, Steve Souders' shows 14 specific rules you can use to squeeze 20% to 25% more speed out of your website. O'Reilly Media, 2007.
Web Performance Tuning: Speeding Up the Web, 2d ed.
Patrick Killelea's primarily server-side how-to on boosting the performance and reliability of websites. O'Reilly Media, 2002.


Theurer, T., and S. Souders. April 11, 2007. "Performance Research, Part 4: Maximizing Parallel Downloads in the Carpool Lane."
Yahoo! Interface Blog, (accessed February 11, 2008). Theurer provided the author with an updated figure.
Breen, R. December 18, 2006. "Circumventing browser connection limits for fun and profit."
Ajax Performance, (accessed February 11, 2008). Figure 9-2 used with permission.
Theurer, T. November 28, 2006. "Performance Research, Part 1: What the 80/20 Rule Tells Us about Reducing HTTP Requests."
Yahoo! User Interface Blog, (accessed February 11, 2008).
Port80 Software. July 2007. "Port80 Surveys HTTP Cache Control on the Top 1000 Corporations' Web Sites."
Port80 Software, (accessed February 11, 2008).
Bent, L. et al. 2004. "Characterization of a Large Web Site Population with Implications for Content Delivery."
In WWW 2004 (New York: May 17-22, 2004), 522-533.
The mod_gzip software for Apache 1.3,
and a link to a 2.x version, are available from SourceForge at http:// A development version of mod_gzip for Apache 2.0 is available at
See Table 18.2, "Content Encoding Average Compression Ratios for Different Web Site Categories,"
in my book Speed Up Your Site: Web Site Optimization (New Riders).
Destounis, P. et al. 2001. "Measuring the mean Web page size and its compression to limit latency and improve download time."
Internet Research 11 (1): 15. Analyzing five popular websites (, Disney. com,,, and, Destounis found a mean compression gain of 75.2% across 9,281 HTML pages. The mean web page size was 13,540 bytes.
Savant, A., and T. Suel. 2004. "Server-Friendly Delta Compression for Efficient Web Access."
In Proc. of the 8th International Workshop on Web Content Caching and Distributing, 303-322.
Mogul, J. et al. 1997. "Potential benefits of delta-encoding and data compression for HTTP."
In SIGCOMM 1997 (Cannes, France: September 14-18, 1997), 181-194.
Mogul, J. et al. January 2002. "Delta encoding in HTTP."
RFC 3229, (accessed February 11, 2008).
Scoble, R. September 8, 2004. "Full text RSS on MSDN gets turned off."
Scobleizer, (accessed February 11, 2008).
Wyman, B. September 13, 2004. "Using RFC3229 with Feeds."
As I May Think, (accessed February 11, 2008).
Wyman, B. October 3, 2004. "Massive Bandwidth Savings proven!"
As I May Think, (accessed February 11, 2008).
Google's "Gears" API includes the ability to run scripts asynchronously in the background.
Available at Google Gears.
Chipman, S.G. September 26, 2005. "09.26.2005-Safari & createElement('script')."
slayeroffice, (accessed February 11, 2008).
Eisenzopf, J. September 1, 1999. "Using RSS News Feeds."
"Mother of Perl" column,, (accessed February 11, 2008).
Masinter, L. August 1998. "The 'data' URL scheme."
RFC 2397, (accessed February 11, 2008).
Lawson, B. December 19, 2007. "IE8 passes Acid2 test."
The Web Standards Project, (accessed February 12, 2008).
For our inline image size comparison,
the folder image was 526 bytes for the Base64 code, versus 409 bytes gzipped, versus 377 bytes for the folder image GIF.
Mozilla Developer Center. February 12, 2007. "The data URL scheme."
Mozilla Foundation, (accessed February 11, 2008).
Herrera, B. March 25, 2005. "A Cross-Browser Method for Embedding Images in Self-Contained HTML Documents.", (accessed February 12, 2008).

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