Distributed Database Management Systems - vu_Lec_16

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

– The set of partitions for owner – Member relation

– Semi-join predicates between owner

and member

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DHA

ASIGN

1- One with better Join Characteristics

2- One used in more applications

should try to facilitate heavy users; the first one needs more

considerations

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

EMP1

PAY2

EMP2

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DHF

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

cases

Disjointness: 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

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]

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Reconstruction:

Involves Union in both cases

FR = {R1,R2,….Rn}

R = U Ri Ri FR ∀ ∈

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

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Vertical Fragmentation (VF)

fragments R1, R2, … Rn, each of which contains subset of attributes

of R and PK of R.

relations, so that most of the

applications run on smaller

relations; so they become fast.

Vertical Fragment

• Vertical fragmentation is more

complicated, since more

alternatives exist.

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Example of VF

A/C# Na

me Bal Branch AB10

1 Saeed 4535 MTN AB20

2 Laeeq 45632.34 LHR AB20

3 Salma 67839.87 LHR AB10

9 Shaan 45.32 MTN

A/C# Na

me Branch AB10

1 Saeed MTN AB20

2 Laeeq LHR AB20

3 Salma LHR AB10

9 Shaan MTN

CUST

A/C# Bal AB10

1 4535 AB20

2 45632.34 AB20

3 67839.87 AB10

9 45.32

Two Alternatives of VF

• Grouping: Starting with single

attribute VFs and then

combining different attributes

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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

non-overlapping fragments; so

discussed here

Thanks