ACID Properties in DBMS
ACID is a set of properties that guarantee that database transactions are processed reliably. These properties are essential in any database system where multiple transactions occur concurrently. ACID stands for Atomicity, Consistency, Isolation, and Durability.
Atomicity refers to the all-or-nothing property of transactions. It means that a transaction is treated as a single unit of work, which is either completed successfully or not completed at all. If any part of the transaction fails, then the entire transaction is rolled back, and the database is returned to its state before the transaction began.
For example, consider a bank transfer transaction that involves debiting one account and crediting another account. If the debit operation is successful but the credit operation fails due to some error, the entire transaction is rolled back, and the original balance of the accounts is restored.
Consistency refers to the property that ensures that a transaction brings the database from one consistent state to another consistent state. A consistent state is a state where all the constraints and rules of the database are satisfied. In other words, a transaction should not violate any constraints or rules defined on the database.
For example, consider a database of a university that contains student records. If a transaction tries to update the GPA of a student to a value that is outside the valid range of GPAs, the transaction will be rolled back, and the database will remain consistent.
Isolation refers to the property that ensures that each transaction is executed independently of other transactions. It means that the result of a transaction should be visible to other transactions only after the transaction has been committed.
For example, consider two transactions that are updating the same record in a database. If the isolation property is not enforced, one transaction may overwrite the changes made by the other transaction, resulting in an inconsistent database state. With isolation, the two transactions can execute concurrently without interfering with each other.
Durability refers to the property that ensures that once a transaction is committed, its effects are permanent and will survive any subsequent system failures. It means that even if the system crashes or loses power, the data modified by a committed transaction will be preserved.
For example, consider a transaction that transfers money between two bank accounts. Once the transaction is committed, the balance of the accounts should be updated permanently, even if there is a power failure or system crash.
The ACID properties are essential for ensuring that database transactions are processed reliably. Atomicity ensures that transactions are treated as a single unit of work. Consistency ensures that transactions bring the database to a consistent state. Isolation ensures that transactions are executed independently of each other. Durability ensures that committed transactions are permanent and will survive any system failures. Together, these properties provide a reliable foundation for building database applications.