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Two newish technical reports based on an HTTP trace

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  • Jeffrey Mogul
    About a year ago, I gathered a long (90-day) proxy trace of HTTP requests, including MD5 digests of the response bodies. (No, you can t get access to this
    Message 1 of 1 , Mar 8, 2000
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      About a year ago, I gathered a long (90-day) proxy trace of
      HTTP requests, including MD5 digests of the response bodies.
      (No, you can't get access to this trace, so please don't even ask.)
      I've finished a pair of technical reports based on this trace:

      "A trace-based analysis of duplicate suppression in HTTP"
      Compaq Western Research Lab Research Report 99/2, November 1999

      Many HTTP resources (pages, graphics, etc.) are exact
      duplicates of other resources with different URLs. If an HTTP
      cache contains a duplicate of a requested resource, and could
      detect this, it could avoid substantial network costs by
      returning the cached duplicate in place of the requested URL.
      Previous studies have shown that there is substantial
      duplication of content in both HTTP and FTP, and several
      protocols have been proposed to support efficient and safe
      duplicate suppression in HTTP. We use traces covering
      millions of HTTP requests to quantify the potential benefit
      of an HTTP duplicate-suppression extension. In particular, we
      show that the benefits vary depending on content-type, and
      that a small fraction of Web servers account for most of the
      duplicated resources.

      for Postscript & PDF format versions

      (2) "Errors in timestamp-based HTTP header values"
      Compaq Western Research Lab Research Report 99/3, December 1999

      Many of the caching mechanism in HTTP, especially in
      HTTP/1.0, depend on header fields that carry absolute
      timestamp values. Errors in these values could lead to
      undetected cache incoherence, or to excessive cache misses.
      Using an extensive proxy trace, we looked for HTTP responses
      exhibiting several different categories of timestamp-related
      errors. A significant fraction of these responses have
      detectable errors in timestamp-based header fields.

      for Postscript & PDF format versions


      P.S.: The astute observer will notice that there is also a
      timestamp error in the date on one of these technical reports; I
      was a bit optimistic about when I would finish it, and then it
      was easier to issue it back-dated than to revise our report
      numbering scheme.
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