Distributed Database Management Systems: Lecture 20

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

–Computed CA

–Partitioning Algorithm

In this Lecture

–Hybrid Fragmentation–Allocation Problem

–Replication

VF Correctness

• A relation R, defined over

attribute set A and key K,

generates the vertical

Hybrid Fragmentation

Practically,

applications require the fragmentation of both the types to be combined

So the nesting of

fragmentations, i.e., one following the

other, it becomes

sort of a tree

• Disjoint ness and

completeness have to

be assured at each

step, and

reconstruction can be obtained by applying Join and Union in

reverse order

A/C# Name Bal Branch

Delta1 =   Loc = “MTN” ( σ ΠA/C#, Name, Branch (CUST))

Beta =  ΠA/C#, Bal (CUST)

Allocation

• Optimality

–Minimize the processing

cost and maximize the

system throughput at

each site

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

The specification of the

allocation problem will be

0 otherwise

x j = 1 if the fragment Fk  is assigned to site Sj

I S j

j j

ij I

s j

j I

Sj j

ij j

j m

d x c

t c

min '

• That concludes our

discussion on

Fragmentation

Horizontal

Fragmentation

• Splits a table into

horizontal subsets (row

wise)

• Primary and Derived

Horizontal Fragmentation

• We need major simple

• Calculated using

usage data and

access frequencies from different sites

into CA using BEA

Thanks