Distributed Database Management Systems: Lecture 16. The main topics covered in this chapter include: the inputs required for DHF; the set of partitions for owner; member relation; semi-join predicates between owner and member;...
Distributed Database Management Systems Lecture 14 DHF • The inputs required for DHF – The set of partitions for owner – Member relation – Semi-join predicates between owner and member Virtual University of Pakistan DHA • Care in case of multiple owners, like ASIGN • Fragmentation selection depends: 1- One with better Join Characteristics 2- One used in more applications • Second one is straight forward, we should try to facilitate heavy users; the first one needs more considerations Virtual University of Pakistan DHF • For the first point; – Join is performed on smaller relations, that increases efficiency – The join can be performed in parallel in case of simple graphs, that improves efficiency as well; simple graph means PAY1 PAY2 EMP1 EMP2 Virtual University of Pakistan DHF • demonstrates two things 1-Derived fragmentation may follow a chain, like PAY-EMP-ASIGN 2-Typically, more than one fragmentation options are there, which one adopted is an allocation problem discussed later Checking for Correctness Completeness: for PHF depends on Pr’, and in DHF, completeness of owner Pr’, and the referential integrity constraint Reconstruction: Involves Union in both Virtual cases University of Pakistan Checking for Correctness Completeness: for PHF depends on Pr’, and in DHF, completeness of owner Pr’, and the referential integrity constraint Let R be member S be owner Fs = { S1,S2,…Sn} ‘A’ the common attribute t[A] = t’ [A] Virtual University of Pakistan Reconstruction: Involves Union in both cases FR = {R1,R2,….Rn} R = U Ri ∀ Ri ∈FR Virtual University of Pakistan Disjoint ness: Simple in PHF if the pi in Pr’ are mutually exclusive; in DHF, guaranteed in case of simple join graph, however in case of partitioned join graph it is hard to establish Virtual University of Pakistan Vertical Fragmentation (VF) • Vertical subset of relation • A VF of a relation produces fragments R1, R2, … Rn, each of which contains subset of attributes of R and PK of R • Objective is to produce smaller relations, so that most of the applications run on smaller relations; so they become fast Virtual University of Pakistan Vertical Fragment • Vertical fragmentation is more complicated, since more alternatives exist • VF is mainly based on heuristics Virtual University of Pakistan 10 Example of VF CUST A/C# Na me Delta = ΠA/C#, Name, Branch (CUST) Beta = ΠA/C#, Bal (CUST) Virtual University of Pakistan AB10 Bal Sae 4535 ed AB20 Lae eq DeltaAB20 Sal ma A/C# Na Bran me AB10chSha an AB10 Sae MTN ed AB20 Lae LHR eq Bran ch MTN 45632 LHR 34 67839 Beta LHR 87A/C# Bal 45.32 AB10MTN 4535 AB20 45632 34 11 Two Alternatives of VF • Grouping: Starting with single attribute VFs and then combining different attributes Virtual University of Pakistan 12 Two Alternatives of VF • Splitting: Starting from the whole relation and then breaking it down analyzing the nature of applications • Later suits better to DDB environment; results nonoverlapping fragments; so discussed here Virtual University of Pakistan 13 Thanks ... EMP2 Virtual University of Pakistan DHF • demonstrates two things 1-Derived fragmentation may follow a chain, like PAY-EMP-ASIGN 2-Typically, more than one fragmentation options are there, which... Member relation – Semi-join predicates between owner and member Virtual University of Pakistan DHA • Care in case of multiple owners, like ASIGN • Fragmentation selection depends: 1- One with better... owners, like ASIGN • Fragmentation selection depends: 1- One with better Join Characteristics 2- One used in more applications • Second one is straight forward, we should try to facilitate heavy