A collection of operations that form a single logical unit of work is called transaction. The operations that make up a transaction typically consists of requests to access existing data, modify existing data, add new data or any combination of these requests. The transaction consists of all operations executed between the begin transaction and end transaction.
ACID Properties of Transaction
To ensure the integrity of data, database system must maintain some desirable properties of the transaction. These properties are known as ACID properties.
Atomicity : Either all the operations that make up a transaction should execute or none of them should occur.
Consistency : The consistency property of a transaction implies that if database was in consistent state before the initiation of transaction, then at the end of transaction the database will also be in a consistent state. It should be noted that during the execution of transaction the state of database becomes inconsistent. Such an inconsistent state of database should not be visible to the users or other concurrently running transactions.
Isolation : It implies that steps or operations performed by a transaction should be isolated from other concurrently running transactions.
Durability : Once a transaction is committed, the changes made by transaction persists in the database, even if there are system failures.
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