Potential benefits of delta encoding and data compression for HTTP

  • Authors:

  • Jeffrey C. Mogul;Fred Douglis;Anja Feldmann;Balachander Krishnamurthy

  • Affiliations:

  • Digital Equipment Corporation Western Research Laboratory, 250 University Avenue, Palo Alto, CA;AT&T Labs - Research, 180 Park Avenue, Florham Park, NJ;AT&T Labs - Research, 180 Park Avenue, Florham Park, NJ;AT&T Labs - Research, 180 Park Avenue, Florham Park, NJ

  • Venue:
  • SIGCOMM '97 Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication
  • Year:
  • 1997

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Abstract

Caching in the World Wide Web currently follows a naive model, which assumes that resources are referenced many times between changes. The model also provides no way to update a cache entry if a resource does change, except by transferring the resource's entire new value. Several previous papers have proposed updating cache entries by transferring only the differences, or "delta," between the cached entry and the current value.In this paper, we make use of dynamic traces of the full contents of HTTP messages to quantify the potential benefits of delta-encoded responses. We show that delta encoding can provide remarkable improvements in response size and response delay for an important subset of HTTP content types. We also show the added benefit of data compression, and that the combination of delta encoding and data compression yields the best results.We propose specific extensions to the HTTP protocol for delta encoding and data compression. These extensions are compatible with existing implementations and specifications, yet allow efficient use of a variety of encoding techniques.