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Updated on June 10, 2010

ACID - The Properties of Database Transactions

Here we discuss database updates known as Transactions.

A Database Transaction can be made up of several operations. However, a transaction is considered to be a single logical operation on a database. For example, a funds transfer transaction consists of two account update operations.

In order to guarantee the reliability of database transactions they must have a specific set of properties denoted by the acronym ACID (Atomicity, Consistency, Isolation and Durability).

The Atomicity property means that all the operations of the transaction must take place as a whole. Either all operations take place or none of them do. If the transaction terminates early, for any reason, then the data is not changed.

The DBMS ensures that the data is consistent after each transaction. By this we mean that the database maintains referential integrity and all of the constraints defined for the database.

A database transaction takes place in Isolation. Other processes within the system will not see the effect of transactions in progress. This ensures that the other processes will not be confused by partially complete transaction. It also ensures that the operations of concurrent transactions are not interleaved.

Once a transaction has completed then its data is secured. The updates will not be lost even after system failure.


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