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
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