‘One of the potential advantages of Distributed Database Management Systems is improved reliability and availability.’
(a) The consistency and reliability aspects of transactions are due to the ‘ACIDity’
properties of transactions. Discuss each of these properties and how they relate to the concurrency control and recovery mechanisms. Give examples to illustrate your answer.
A – Atomicity; all-or-nothing property; part of recovery control
C – Consistency (correctness); a transaction is a correct program that maps a database from
one consistent database state to another; part of concurrency control
I – Isolation; requires each transaction to see a consistent database at all times; part of concurrency control
D – Durability; ensures that once a transaction commits, its results are permanent and cannot be erased from the database; part of recovery control
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