Distributed Database Management Systems - vu_Lec_16

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

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2


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
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3


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

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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
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5


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

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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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8


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.
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Vertical Fragment
• Vertical fragmentation is more
complicated, since more
alternatives exist.
• VF is mainly based on heuristics

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10


Example of VF
CUST

A/C# Na
me
Delta = ΠA/C#, Name, Branch (CUST)
Beta =  ΠA/C#, Bal (CUST)

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AB10
1

Bal

Sae 4535
ed

AB20 Lae
2
eq
DeltaAB20 Sal
3
ma
A/C# Na
Bran
me
AB10chSha
9
an
AB10 Sae
MTN
1
ed
AB20 Lae LHR
2
eq

Bran
ch
MTN

45632 LHR
.34
67839 Beta
LHR
.87A/C# Bal
45.32
AB10MTN
4535
1
AB20 45632
2
.34

11


Two Alternatives of VF
• Grouping: Starting with single
attribute VFs and then
combining different attributes

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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
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13


Thanks