ACID property

In this article I am trying to describe the ACID property of the database in a short and simple manner. Hope you like it.

The AICD stands for

1.    Atomicity

2.    Consistency

3.    Isolation

4.    Durability

Let's describe each to understand it properly.

Atomicity

Modification of the data in the database, either failure or success. The begin of the such modifications starts with BEGIN TRANSACTION and ends with COMMIT TRANSACTION or ROLLBACK TRANSACTION.

BEGIN

  BEGIN TRY

        BEGIN TRANSACTION

        <..........>

        COMMIT TRANSACTION

  END TRY

  BEGIN CATCH

        <..........>

        ROLLBACK TRANSACTION

  END CATCH

END

Features to consider for atomicity:

• a transaction is a unit of operation - either all the transaction's actions are completed or none are
• atomicity is maintained in the presence of deadlocks
• atomicity is maintained in the presence of database software failures
• atomicity is maintained in the presence of application software failures
• atomicity is maintained in the presence of CPU failures
• atomicity is maintained in the presence of disk failures
• atomicity can be turned off at the system level
• atomicity can be turned off at the session level

Consistency

Only the valid data according to integrity constraints may be committed.

Isolation

One transaction does not interact with others.

  

Durability

When a transaction is committed the data will not be lost.

Features to consider for durability:

• recovery to the most recent successful commit after a database software failure
• recovery to the most recent successful commit after an application software failure
• recovery to the most recent successful commit after a CPU failure
• recovery to the most recent successful backup after a disk failure
• recovery to the most recent successful commit after a data disk failure 

Posted by: MR. JOYDEEP DAS