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On Random Sampling over Joins

Spring - 2007 CSE 6392 – 003 Data Exploration and Analysis in Relational Databases. On Random Sampling over Joins. Surajit Chaudhuri Rajeev Motwani Vivek Narasayya. By: Lekhendro 2/27/2007. Outlines. Semantic and algorithms of sample The difficulty of join sampling

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On Random Sampling over Joins

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  1. Spring - 2007 CSE 6392 – 003 Data Exploration and Analysis in Relational Databases On Random Sampling over Joins Surajit Chaudhuri Rajeev Motwani Vivek Narasayya By: Lekhendro 2/27/2007

  2. Outlines • Semantic and algorithms of sample • The difficulty of join sampling • Classification of Join problems • Two previous sampling strategies • New strategies for join sampling • Experiment results

  3. Semantics of Sampling • Sampling with Replacement (WR) • Sampling without Replacement (WoR) • Independent Coin Flips (CF) • Stream Sampling • Sequential • Non sequential (could be on materialized data) • Weighted and Unweighted Sampling

  4. I. Black-Box U1: Given relation R with n tuples, generate an UNWEIGHTED WR sample of size r. Sequential WR Sampling

  5. II. Black-Box U2: Given relation R with n tuples, generate an UNWEIGHTED WR sample of size r. Sequential WR Sampling: continued…

  6. III. Black-Box WR1: Given relation R with n tuples, generate an WEIGHTED WR sample of size r. Sequential WR Sampling:continued…

  7. IV. Black-Box WR2: Given relation R with n tuples, generate an WEIGHTED WR sample of size r. Sequential WR Sampling:continued…

  8. The Difficulty of Join Sampling • Suppose that we have the relations

  9. Classification of the Problem: Case A :No information is available for either or . Case B : No information is available for but indexes and /or statistics are available for . Case C : Indexes/statistics are available for and .

  10. Previous Sampling Strategies I.Strategy Naive-Sample:

  11. Previous Strategies: continued… II.Strategy Olken-Sample:

  12. New Strategies for Join Sampling I. Strategy Stream Sample:

  13. New Strategies: continued … II. Strategy Group Sample

  14. New Strategy : continued … III.Strategy Frequency-Partition-Sample

  15. Experimental Results:

  16. Experimental Results:

  17. Experimental Results:

  18. Summary • The difficulty of join sampling. • Classification of problem for random sampling over join – 3 cases. • Different strategies:

  19. Summary : continued … • When indexes/statistics are NOT provided in both operands • Frequency Partition Strategy outperformed others strategies. • When indexes/statistics areprovided in both operands • Stream strategy is the best among them. • Stream strategy is also applicable when indexes/statistics areavailable only in the inner relation

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