Distributed Database Management Systems: Lecture 20. The main topics covered in this chapter include: continue with VF to hybrid fragmentation; allocation problem; replication; VF correctness; primary and derived horizontal fragmentation;...
Distributed Database Management Systems Lecture 20 In the Previous Lecture • Continued with VF –Computed CA –Partitioning Algorithm In this Lecture • Continue with VF –Hybrid Fragmentation –Allocation Problem –Replication A1 A3 A2 A4 A1 45 45 0 A3 45 53 A2 A4 75 78 CA 80 75 A1 A2 A3 A4 S1 S2 S3 q1 1 q1 15 20 10 q2 1 q2 q3 1 q3 25 25 25 q4 0 1 refj(qi) z2 = 3311 z1 = 0 – 452 z3= 0 78 0 q4 0 accj(qi) A1= jNo A2= jName A3= budget A4= loc V1 = {jNo, budget} V2 = {jNo, jName, loc} VF- Two Problems 1- Clusters not in the sides, rather in the middle of CA 2- m-way partitioning VF Correctness • A relation R, defined over attribute set A and key K, generates the vertical partitioning • FR = {R1, R2 , …, Rr } • Completeness: The following should be true for A A =U Ri • Reconstruction: can be achieved by R = ⋈K Ri, ∀Ri ∈ FR • Disjointness: TID's are not considered to be overlapping since they are maintained by the system • PK is exception Hybrid Fragmentation It is a complex problem to be solved mathematically, to make the things very simple, consider the allocation of a single fragment Fk, • set of read only queries on Fk from Si; T = {t1, t2, …, tm} • set of update queries U on Fk from Si; U= {u1, u2, , um} Communication Cost C(T) = {c1,2, c1,3, …., c1,m, ….cm-1, m} C’(T) = {c’1,2, c’1,3, …., c’1,m, ….c’m-1, m} Storage Cost D = {d1, d2, ……., dm} Allocation problem is to find the cites out of set of sites S, where the copy of Fk will be stored 1 if the fragment Fk is assigned to site Sj xj = 0 otherwise The specification of the allocation problem will be min m i xjujc ' ij j|Sj I tj cij j|sj I xjdj j|Sj I • That concludes our discussion on Fragmentation • Lets summarize it • Fragmentation is splitting a table into smaller tables • Alternatives – Horizontal –Vertical –Hybrid Horizontal Fragmentation • Splits a table into horizontal subsets (row wise) • Primary and Derived Horizontal Fragmentation • We need major simple predicates (Pr); should be complete & minimal • Pr is transformed into Pr’ • Minterm (M) predicates from Pr’ • Correctness of PHF depends on the Pr’ • Derived Horizontal Fragmentation is based on Owner-member link • Vertical Fragmentation is more complicated due to more options • Based on attributes’ affinities • Calculated using usage data and access frequencies from different sites • AA is transformed into CA using BEA • CA establishes clusters of attributes that are split for efficient access • Hybrid Fragmentation combines HF and VF • That concludes Fragmentation Thanks ... A/C# Bal AB101 4535 A/C# Name Branch A/C# Name Branch AB202 45632.34 AB101 Saeed MTN AB202 Laeeq LHR AB203 67839.87 AB109 Shaan MTN AB203 Salma LHR AB109 45.32 Allocation • Given F = {F1, F2... obtained by applying Join and Union in reverse order CUST Beta = ΠA/C#, Bal (CUST) A/C# AB101 AB202 AB203 AB109 Name Saeed Laeeq Salma Shaan Bal 4535 45632.34 67839.87 45.32 Branch MTN LHR LHR MTN...In the Previous Lecture • Continued with VF –Computed CA –Partitioning Algorithm In this Lecture • Continue with VF –Hybrid Fragmentation –Allocation