Distributed Databases Dr. Lee By Alex Genadinik

Distributed Databases? What is that!?? Distributed Database - a collection of multiple logically interrelated databases distributed over a computer network

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.

Visual Representation

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

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

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)

Architecture, Visually

More of Conceptual View

2 Basic Patterns Horizontal – Store Whole Tuples on Different machines. Vertical – Store Different Fields of the same tuples on Different machines.

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:  ”new  york” (City)  “chicago” (City)

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

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.

Cont.. Each database in a distributed database is distinct from all other databases in the system and has its own global database name

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”;

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.

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.

Case Study cont.. If the two users needed to use the company’s 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 wouldn’t be able to see them and would be working with an outdated database.

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.

Conclusion cont.. Thank you everyone for your Attention. ~ Alex