ACID is a set of properties that ensure reliable transactions in a database system. These properties are essential for maintaining the integrity and consistency of the database. ACID stands for:
- Atomicity:
- Definition: A transaction is an atomic unit of work, which means it is indivisible. It either completes in its entirety or does not happen at all.
- Example: If a transaction involves transferring money from one account to another, atomicity ensures that both the debit and credit operations occur together. If one operation fails, the entire transaction is rolled back.
- Consistency:
- Definition: A transaction must transition the database from one consistent state to another. This means that the database should adhere to all predefined rules, constraints, and integrity checks before and after the transaction.
- Example: If a transaction updates data in a way that violates a database constraint (e.g., a unique key constraint), the transaction will not be allowed to commit, ensuring that the database remains consistent.
- Isolation:
- Definition: Transactions should operate independently of each other, meaning the operations of one transaction should not be visible to other transactions until the transaction is committed.
- Example: If two transactions are executed concurrently, isolation ensures that each transaction is unaware of the other until both are completed. This prevents issues such as dirty reads, non-repeatable reads, and phantom reads.
- Durability:
- Definition: Once a transaction is committed, its changes are permanent and should survive any subsequent system failures or crashes.
- Example: After a successful transaction, the changes made to the database (e.g., updating a record) are saved and will be available even if the database system crashes immediately after the commit.
Why ACID Properties Matter
- Reliability: Ensures that database transactions are processed reliably and consistently.
- Data Integrity: Prevents data corruption and maintains accuracy.
- Concurrency Control: Manages multiple transactions occurring simultaneously without interference.
- System Recovery: Protects data integrity and consistency in case of failures or crashes.
Together, these properties provide a robust framework for handling transactions in database systems, ensuring data reliability and consistency in various scenarios.