A transaction in a database system must maintain Atomicity, Consistency, Isolation, and Durability − commonly known as ACID property − in order to ensure accuracy, completeness, and data integrity.
- Atomicity
- Consistency
- Isolation
- Durability
Atomicity: –
- A transaction is an atomic unit of processing.
- It is either performed entirely or not performed at all.
- Means either all operations are reflected in the database or none are.
- It is the responsibility of the transaction recovery subsystem to ensure atomicity.
- moreover, If a transaction fails to complete for some reason, the recovery technique must undo any effects of the transaction on the database.
Consistency: –
- A transaction is consistency preserving if its complete execution takes the database from one consistent state to another.
- It is the responsibility of the programmer who writes database programs.
- Database programs should be written in such a way that, if the database is in a consistent state before execution of transaction. After That it will be in a consistent state after execution of transaction.
- For instance, Transaction is :- Transfer $50 from account A to account B.
- If account A having amount $100 & account B having amount $ 200 initially then after execution of transaction, A must have $ 50 & B must have $ 250.
Isolation: –
- If multiple transactions execute concurrently. They should produce the result as if they are working serially.
- Further, It is enforce a concurrency control subsystem.
- To avoid the problem of concurrent execution, transactions should be executed in isolation.
Durability: –
- The changes applied to the database, by a committed transaction must persist in a database.
- The changes may not be lost because of any failure.
- It is the responsibility of the recovery subsystem of the DBMS.
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