Distributed Databases

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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 distributed over
  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 DBMS must 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 Recovery and
  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 complicated
  security 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 the same
  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 multiple copies
  of data from user
• Fragmentation Transparency Hide the fact that
  data is fragmented (ie, different sections of
  correlated data may be in different locations)

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Architecture, Visually
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More of Conceptual 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 a
  restriction on a relation that creates these
• snew york (City)
• s chicago (City) 

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Vertical pattern

• Store Different Fields of the same tuples on
  Different machines
• Use Projection Op to declare these
•  P (Acct , Branch, Client Name Account)
•  P (Acct , Balance Account) 
• (requires redundant storage of at least one
  primary key per tuple) 

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Few Comments Before Moving On

• Data is completely dispersed
• Data is replicated (helps in case of accidents)
• 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 data that
  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 the companys
  database and make changes to some data, they
  needed to have the database centralized
  somewhere.
• They could not make changes to the database
  because the other person wouldnt be able to see
  them and would be working 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