Abbreviate ACID - Database - Atomicity, Consistency, Isolation, Durability

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• Nirja Shah   -Posted on 30 Oct 15
  - A transaction is a very small unit of a program and it may contain several lowlevel tasks.
  
  - A transaction in a database system must maintain Atomicity, Consistency, Isolation, and Durability - commonly known as ACID properties - in order to ensure accuracy, completeness, and data integrity.
  
  Atomicity
  - This property states that a transaction must be treated as an atomic unit, that is, either all of its operations are executed or none.
  - There must be no state in a database where a transaction is left partially completed.
  - The states should be defined either before the execution of the transaction or after the execution/abortion/failure of the transaction.
  
  Consistency
  - The database must remain in a consistent state after any transaction.
  - There should be no adverse effect on the data residing in the database by any transaction.
  - If the database was in a consistent state before the execution of a transaction, it must remain consistent after the execution of the transaction as well.
  
  Durability
  - The database should be durable enough to hold all its latest updates even if the system fails or restarts.
  - The database will hold the modified data if a transaction updates a chunk of data in a database and commits.
  - Data will be updated once the system springs back into action if a transaction commits but the system fails before the data could be written on to the disk.
  
  Isolation
  - In a database system where more than one transaction are being executed simultaneously and in parallel, the property of isolation states that all the transactions will be carried out and executed as if it is the only transaction in the system.
  - No transaction will affect the existence of any other transaction.
  

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