Distributed Databases Presentation

8/6/2019 Distributed Databases Presentation

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Distributed Databases

Dr. Lee

By Alex Genadinik


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Distributed Databases? What is

that!?? Distributed Database - a collection of

multiple logically interrelated databases

distributedover a computer network


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Overview

Because the database is distributed,

different users can access it without

interfering with one another.

However, the DBMSmust periodically

synchronize the scattered databases to

make sure that they all have consistent

data.


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Visual Representation


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More Detailed List of Benefits

No centralized point of failure (data is not

centralized).

Local autonomy Ability to distribute data over multiple

storage drives (no supercomputers)

Replication of Data for Disaster Recoveryand High Availability


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Closer look at the drawbacks

Increased complexity of database design,

hardware and other software

Gives rise to absolute need of complicatedsecurity software and procedures

Requires resolution for concurrent

operation as well as having data integrity

issues


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System Transparency

Location Transparency A command works thesame no matter where in the system it is issued

Naming Transparency We can refer to data by

the same name, from anywhere in the system,with no further specification.

Replication Transparency Hides multiplecopies of data from user

Fragmentation Transparency Hide the fact thatdata is fragmented (ie, different sections ofcorrelated data may be in different locations)


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Architecture, Visually


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More ofConceptual View


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2 Basic Patterns

Horizontal Store

Whole Tuples on

Different machines.

Vertical Store

Different Fields of the

same tuples on

Different machines.


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Horizontal pattern

Entire tuples are on different machines

This is nice because we can use standard

relational algebra statements to define arestriction on a relation that creates these:

Wnew york (City)W chicago (City)


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Vertical pattern

Store Different Fields of the same tuples

on Different machines

Use Projection Op to declare these:4 (Acct #, Branch, Client Name Account)

4 (Acct #, Balance Account)

(requires redundant storage of at least oneprimary key per tuple)


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Few Comments Before Moving On

Data is completely dispersed

Data is replicated (helps in case ofaccidents)

There is no global directory

Local-Master Directory

Each node has its own catalog of data

Each node has a directory to all of its datathat is replicated elsewhere.


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Cont..

Each database in a distributed database is

distinct from all other databases in the

system and has its own global database

name


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Name Resolution

Every data object in every schema in

every database has a unique identifying

name

SELECT * FROM Some Remote

Database with a unique name WHERE

X;


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Remote and Distributed SQL

Statements

Remote update modification of data in

one or more tables (all tables located on

the same remote node).

Remote query - retrieves information from

two or more nodes.


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Case Study

One may think distributed databases are

required in large corporations that have

large databases. This is not true.

Sometimes even in a single office, with

only two cubicles that have two computers

you may need to have your database on a

network i.e., distributed.


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Case Study cont..

If the two users needed to use thecompanys database and make changesto some data, they needed to have the

database centralized somewhere.

They could not make changes to the

database because the other personwouldnt be able to see them and would beworking with an outdated database.


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Conclusion

If you are not running a simple database

that is local to only your workstation, you

need to be using a database that is on

some server i.e., a distributed database.


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Conclusion cont..

Thank you everyone for your

Attention.

~ Alex

Distributed Databases Presentation

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