What is a transaction and what are the ACID properties of a transaction?

A Transaction is a sequence of operations performed as a single logical unit, which must be fully completed or fully rolled back.

Transaction Properties (ACID):

Atomicity:

• A transaction is fully completed or not executed at all.
• If a failure occurs, all changes are rolled back.

Consistency:

• A transaction transitions the database from one consistent state to another.
• All database rules and constraints are maintained.

Isolation:

• The results of a transaction are invisible to other transactions until it is completed.
• Prevents interference between concurrent transactions.

Durability:

• Once a transaction is successfully completed, its results are permanently saved, even in the event of system failures.
• Changes are written to persistent storage.