What are ACID properties in databases?

ACID is a set of properties that guarantee reliable transactions in databases:

• Atomicity: a transaction is completed in full or not at all. If something goes wrong, all changes are rolled back.
• Consistency: after a transaction completes, the database remains in a correct state, satisfying all rules and constraints.
• Isolation: parallel transactions do not affect each other, as if they were executed sequentially.
• Durability: after a transaction is committed, changes are saved and not lost even in case of failures.

For example, in transferring money between accounts:

• Atomicity guarantees that debit and credit happen together or not at all.
• Consistency ensures account balances do not become negative if prohibited.
• Isolation means other operations do not see intermediate states.
• Durability ensures data is saved even if the server crashes after the transaction is committed.