Monday, August 20, 2012

What is Transaction

Transaction is a unit of work that is performed against a database.

For example- if you are creating a record or updating a record or deleting a record from the table then you are performing transaction on the table. It is important to control transactions to ensure data integrity and tohandle database errors.

Properties of Transactions:

Atomicity requires that each transaction is "all or nothing": If one part of the transaction fails, the entire transaction fails, And the database state is left unchanged. An atomic system must guarantee atomicity in each and every situation, including power failures, errors, and crashes.
or
Atomicity is that  transaction is "all or nothing": if one part of the transaction fails, the entire transaction fails, and the database state is left unchanged. An atomic system must guarantee atomicity in each and every situation, including power failures, errors, and crashes.


Consistency property ensures that any transaction will bring the database from one valid state to another. Any data written to the database must be valid according to all defined rules, including but not limited to constraints, cascades, triggers, and any combination thereof.
or
ensures that the database properly changes states upon a successfully committed transaction.

 Isolation property ensures that the concurrent execution of transactions results in a system state that could have been obtained if transactions are executed serially, i.e. one after the other.

Durability means that once a transaction has been committed, it will remain so, even in the event of power loss, crashes, or errors. In a relational database, for instance, once a group of SQL statements execute, the results need to be stored permanently.

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