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Distributed Database Management Systems

Distributed Database Management Systems. Lecture 15. PHF- Minimality of Pr. A relevant predicate is the one if it influences how fragmentation is performed (fragments f into f i and f j ) then there should be at least one application that accesses f i and f j differently.

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Distributed Database Management Systems

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  1. Distributed Database Management Systems Lecture 15

  2. PHF- Minimality of Pr Virtual University of Pakistan

  3. A relevant predicate is the one if it influences how fragmentation is performed (fragments f into fi and fj) then there should be at least one application that accesses fi and fj differently. Virtual University of Pakistan

  4. If all predicates in a set Pr are relevant then the set is minimal Virtual University of Pakistan

  5. PHF-COM-MIN Algorithm Virtual University of Pakistan

  6. Given: a relation R and a set of simple predicates Pr. • Output: a complete and minimal set of simple predicates Pr’ for Pr. Virtual University of Pakistan

  7. Rule 1: a relation or fragment is partitioned into at least two parts which are accessed differently by at least one application. Virtual University of Pakistan

  8. 1-Initialization: • Find a pi∈ Pr such that pi, partitions R according to Rule 1 Pr’ ← pi Pr ← Pr – pi Virtual University of Pakistan

  9. 2- Iteratively add predicates to Pr' until it is complete, find a pj ∈ Pr such that pjpartitions R according to Rule 1 set Pr' = Pr' U pi; Pr = Pr – pi; Virtual University of Pakistan

  10. if pk in Pr' is non-relevant then Pr' = Pr' – pk Virtual University of Pakistan

  11. Primary Horizontal Partitioning Algorithm Virtual University of Pakistan

  12. Makes use of COM_MIN to perform fragmentation • Input: a relation R and a set of simple predicates Pr Virtual University of Pakistan

  13. Output: a set of minterm predicates M according to which relation R is to be fragmented Virtual University of Pakistan

  14. Pr‘ ← COM_MIN (R,Pr) • determine the set M of minterm predicates Virtual University of Pakistan

  15. determine the set I of implications among pi Pr • eliminate the contradictory minterms from M Virtual University of Pakistan

  16. PHF – Example II Virtual University of Pakistan

  17. 1 Find the name and budget of projects given their no. issued at three sites • p1 : LOC = "Lahore” • p2 : LOC = “Rawalpindi" • p3 : LOC = "Peshawar“ Virtual University of Pakistan

  18. 2 Access project information according to budge one site accesses ≤ 200000 other accesses >200000 • p4 : BUDGET ≤ 200000 • p5 : BUDGET > 200000 Virtual University of Pakistan

  19. Pr = Pr' = {p1 ,p2 ,p3 ,p4 ,p5 } • Implications • p1 p2 p3 • p4 p5 Virtual University of Pakistan

  20. From predicates p1 to p6 in Pr’, there may be so many minterm predicates, like, p1 ^ p2 ^ p3 ^ p4 ^ p5 Excluding the contradicting minterm predicates Virtual University of Pakistan

  21. m1 : (LOC = "Lahore") ^ (BUDGET ≤ 2M) • m2 : (LOC = "Lahore") ^ (BUDGET > 2M) • m3 : (LOC = " Rawalpindi ") ^ (BUDGET ≤ 2M) • m4 : (LOC = "Rawalpindi") ^ (BUDGET > 2M) • m5 : (LOC = "Peshawar") ^ (BUDGET ≤ 2M) • m6 : (LOC = "Peshawar") ^ (BUDGET > 2M) Virtual University of Pakistan

  22. Implications must be based on the database semantics not on a particular extension of the database Virtual University of Pakistan

  23. PROJ Virtual University of Pakistan

  24. Virtual University of Pakistan

  25. Derived Horizontal Fragmentation(DHF) Virtual University of Pakistan

  26. Defined on a member relation of a link according to a selection operation specified on its owner Virtual University of Pakistan

  27. Two important points: • Each link is an equi-join. • Equijoin can be implemented by means of semi-joins Virtual University of Pakistan

  28. So we are interested in defining the partitions of member based on fragmentation of its owner, but want to see attributes only from member, so Virtual University of Pakistan

  29. Ri = R ⋉ Si, 1≤ i ≤ w where w is the maximum number of fragments that will be defined on R and Si =  Fi (S), where Fi is formula for PHF on S Virtual University of Pakistan

  30. DHF Example Virtual University of Pakistan

  31. PAY title, sal EMP eNo, Name, titke jNo, jName, budget, loc PROJ eNo, jNo, resp, dur ASIGN L1 Virtual University of Pakistan

  32. Considering the link L1 above: • owner (L1) = PAY member (L1) = EMP • We want to group employees on the basis of their salaries one with salary less than or equal to 30,000/- and other more than that Virtual University of Pakistan

  33. Virtual University of Pakistan

  34. Virtual University of Pakistan

  35. Virtual University of Pakistan

  36. Thanks

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