Pruning policies for two-tiered inverted index with correctness guarantee

ABSTRACT

The Web search engines maintain large-scale inverted indexes which are queried thousands of times per second by users eager for information. In order to cope with the vast amounts of query loads, search engines prune their index to keep documents that are likely to be returned as top results, and use this pruned index to compute the first batches of results. While this approach can improve performance by reducing the size of the index, if we compute the top results only from the pruned index we may notice a significant degradation in the result quality: if a document should be in the top results but was not included in the pruned index, it will be placed behind the results computed from the pruned index. Given the fierce competition in the online search market, this phenomenon is clearly undesirable.

In this paper, we study how we can avoid any degradation of result quality due to the pruning-based performance optimization, while still realizing most of its benefit. Our contribution is a number of modifications in the pruning techniques for creating the pruned index and a new result computation algorithm that guarantees that the top-matching pages are always placed at the top search results, even though we are computing the first batch from the pruned index most of the time. We also show how to determine the optimal size of a pruned index and we experimentally evaluate our algorithms on a collection of 130 million Web pages.

REFERENCES

• 1: Vo Ngoc Anh , Owen de Kretser , Alistair Moffat, Vector-space ranking with effective early termination, Proceedings of the 24th annual international ACM SIGIR conference on Research and development in information retrieval, p.35-42, September 2001, New Orleans, Louisiana, United States [doi>10.1145/383952.383957]
• 2: Vo Ngoc Anh , Alistair Moffat, Pruning strategies for mixed-mode querying, Proceedings of the 15th ACM international conference on Information and knowledge management, November 06-11, 2006, Arlington, Virginia, USA [doi>10.1145/1183614.1183645]
• 3: Ricardo A. Baeza-Yates , Berthier Ribeiro-Neto, Modern Information Retrieval, Addison-Wesley Longman Publishing Co., Inc., Boston, MA, 1999
• 4: N. Bruno, L. Gravano, and A. Marian. Evaluating top-k queries over web-accessible databases. In ICDE, 2002.
• 5: S. Büttcher and C. L. A. Clarke. A document-centric approach to static index pruning in text retrieval systems. In CIKM, 2006.
• 6: Brendon Cahoon , Kathryn S. McKinley , Zhihong Lu, Evaluating the performance of distributed architectures for information retrieval using a variety of workloads, ACM Transactions on Information Systems (TOIS), v.18 n.1, p.1-43, Jan. 2000 [doi>10.1145/333135.333136]
• 7: David Carmel , Doron Cohen , Ronald Fagin , Eitan Farchi , Michael Herscovici , Yoelle S. Maarek , Aya Soffer, Static index pruning for information retrieval systems, Proceedings of the 24th annual international ACM SIGIR conference on Research and development in information retrieval, p.43-50, September 2001, New Orleans, Louisiana, United States [doi>10.1145/383952.383958]
• 8: Surajit Chaudhuri , Luis Gravano, Optimizing queries over multimedia repositories, Proceedings of the 1996 ACM SIGMOD international conference on Management of data, p.91-102, June 04-06, 1996, Montreal, Quebec, Canada
• 9: Thomas H. Cormen , Clifford Stein , Ronald L. Rivest , Charles E. Leiserson, Introduction to Algorithms, McGraw-Hill Higher Education, 2001
• 10: Open directory. http://www.dmoz.org.
• 11: Ronald Fagin, Combining fuzzy information: an overview, ACM SIGMOD Record, v.31 n.2, June 2002 [doi>10.1145/565117.565143]
• 12: Ronald Fagin , Amnon Lotem , Moni Naor, Optimal aggregation algorithms for middleware, Proceedings of the twentieth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems, p.102-113, May 2001, Santa Barbara, California, United States [doi>10.1145/375551.375567]
• 13: A. Gulli , A. Signorini, The indexable web is more than 11.5 billion pages, Special interest tracks and posters of the 14th international conference on World Wide Web, May 10-14, 2005, Chiba, Japan [doi>10.1145/1062745.1062789]
• 14: Towards Efficient Multi-Feature Queries in Heterogeneous Environments, Proceedings of the International Conference on Information Technology: Coding and Computing, p.622, April 02-04, 2001
• 15: Zoltán Gyöngyi , Hector Garcia-Molina , Jan Pedersen, Combating web spam with trustrank, Proceedings of the Thirtieth international conference on Very large data bases, p.576-587, August 31-September 03, 2004, Toronto, Canada
• 16: B. J. Jansen and A. Spink. An analysis of web documents retrieved and viewed. In International Conf. on Internet Computing, 2003.
• 17: Jon M. Kleinberg, Authoritative sources in a hyperlinked environment, Journal of the ACM (JACM), v.46 n.5, p.604-632, Sept. 1999 [doi>10.1145/324133.324140]
• 18: Ronny Lempel , Shlomo Moran, Predictive caching and prefetching of query results in search engines, Proceedings of the 12th international conference on World Wide Web, May 20-24, 2003, Budapest, Hungary [doi>10.1145/775152.775156]
• 19: Ronny Lempel , Shlomo Moran, Optimizing result prefetching in web search engines with segmented indices, ACM Transactions on Internet Technology (TOIT), v.4 n.1, p.31-59, February 2004 [doi>10.1145/967030.967032]
• 20: Xiaohui Long , Torsten Suel, Optimized query execution in large search engines with global page ordering, Proceedings of the 29th international conference on Very large data bases, p.129-140, September 09-12, 2003, Berlin, Germany
• 21: Xiaohui Long , Torsten Suel, Three-level caching for efficient query processing in large Web search engines, Proceedings of the 14th international conference on World Wide Web, May 10-14, 2005, Chiba, Japan [doi>10.1145/1060745.1060785]
• 22: Looksmart inc. http://www.looksmart.com.
• 23: Sergey Melink , Sriram Raghavan , Beverly Yang , Hector Garcia-Molina, Building a distributed full-text index for the web, ACM Transactions on Information Systems (TOIS), v.19 n.3, p.217-241, July 2001 [doi>10.1145/502115.502116]
• 24: Alexandros Ntoulas , Junghoo Cho , Christopher Olston, What's new on the web?: the evolution of the web from a search engine perspective, Proceedings of the 13th international conference on World Wide Web, May 17-20, 2004, New York, NY, USA [doi>10.1145/988672.988674]
• 25: Alexandros Ntoulas , Marc Najork , Mark Manasse , Dennis Fetterly, Detecting spam web pages through content analysis, Proceedings of the 15th international conference on World Wide Web, May 23-26, 2006, Edinburgh, Scotland [doi>10.1145/1135777.1135794]
• 26: L. Page, S. Brin, R. Motwani, and T. Winograd. The pagerank citation ranking: Bringing order to the web. Technical report, Stanford University.
• 27: Michael Persin , Justin Zobel , Ron Sacks-Davis, Filtered document retrieval with frequency-sorted indexes, Journal of the American Society for Information Science, v.47 n.10, p.749-764, Oct. 1996 [doi>10.1002/(SICI)1097-4571(199610)47:10<749::AID-ASI3>3.3.CO;2-U]
• 28: M. Richardson and P. Domingos. The intelligent surfer: Probabilistic combination of link and content information in pagerank. In Advances in Neural Information Processing Systems, 2002.
• 29: S. Robertson and K. Spärck-Jones. Relevance weighting of search terms. Journal of the American Society for Information Science, 27:129--46, 1976.
• 30: Gerard Salton , Michael J. McGill, Introduction to Modern Information Retrieval, McGraw-Hill, Inc., New York, NY, 1986
• 31: Paricia Correia Saraiva , Edleno Silva de Moura , Novio Ziviani , Wagner Meira , Rodrigo Fonseca , Berthier Riberio-Neto, Rank-preserving two-level caching for scalable search engines, Proceedings of the 24th annual international ACM SIGIR conference on Research and development in information retrieval, p.51-58, September 2001, New Orleans, Louisiana, United States [doi>10.1145/383952.383959]
• 32: Martin Theobald , Gerhard Weikum , Ralf Schenkel, Top-k query evaluation with probabilistic guarantees, Proceedings of the Thirtieth international conference on Very large data bases, p.648-659, August 31-September 03, 2004, Toronto, Canada
• 33: Anthony Tomasic , Hector Garcia-Molina, Performance of inverted indices in shared-nothing distributed text document informatioon retrieval systems, Proceedings of the second international conference on Parallel and distributed information systems, p.8-17, January 1993, San Diego, California, United States

INDEX TERMS

Primary Classification:
  H. Information Systems
  H.3 INFORMATION STORAGE AND RETRIEVAL
      H.3.1 Content Analysis and Indexing

Additional Classification:
  H. Information Systems
  H.3 INFORMATION STORAGE AND RETRIEVAL
      H.3.3 Information Search and Retrieval

General Terms:
Algorithms, Design, Experimentation, Measurement, Performance

Keywords:
correctness guarantee, inverted index, pruning, web search engines