On caching effectiveness of web clusters under persistent connections

  • Authors:

  • Xueyan Tang;Samuel T. Chanson

  • Affiliations:

  • Department of Computer Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong and School of Computer Engineering, Nanyang Technological University, Singap ...;Department of Computer Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong

  • Venue:
  • Journal of Parallel and Distributed Computing - Scalable web services and architecture
  • Year:
  • 2003

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Abstract

Due to the emergence of the HTTP/1.1 standards, persistent connections are increasingly being used in web retrieval. This paper studies the caching performance of web clusters under persistent connections, focusing on the difference between session-grained and request-grained allocation strategies adopted by the web switch. It is shown that the content-based algorithm considerably improves caching performance over the content-blind algorithm at the request-grained level. However, most of the performance gain is offset by the allocation dependency that arises when the content-based algorithm is used at the session-grained level. The performance loss increases with cluster size and connection holding time. An optimization problem is formulated to investigate the best achievable caching performance under session-grained allocation. Based on a heuristic approach, a session-affinity aware algorithm is presented that makes use of the correlation between the requests in a session. Experimental results show that while the session-affinity aware algorithm outperforms the content-based algorithm under session-grained allocation, this optimization cannot fully compensate for the performance loss caused by allocation dependency.