Introduction to Transactions and Their Properties (ACID)

When working with databases, transactions play a significant role in ensuring data integrity and consistency. A transaction is a logical unit of work that consists of multiple database operations bundled together. The concept of transactions is crucial for Database Management Systems (DBMS) as it ensures that all or none of the database operations within a transaction are executed.

The properties of a transaction, commonly referred to as ACID properties, are essential to guarantee the reliability and validity of the database. Let's dive deeper into each of these properties:


Atomicity refers to the indivisibility of a transaction. It ensures that either all the operations within a transaction are successfully completed, or in case of any failure, the transaction is rolled back, and none of its operations are persisted. In other words, a transaction is said to be atomic if it is treated as a single, indivisible unit.

For example, consider a banking scenario where a customer wants to transfer funds from one account to another. When transferring money, different operations need to be performed, such as deducting the amount from the sender's account and adding it to the recipient's account. If any of these operations fail, the entire transaction should be rolled back to the initial state.


Consistency ensures that a transaction brings the database from one consistent state to another. It means that the applied transaction should follow predefined database rules and constraints, maintaining data integrity. If a transaction violates any integrity constraints or leads to an inconsistent state, it is rolled back.

For instance, let's consider a scenario where a student registers for a course. The registration process should ensure that the student's prerequisites are met, such as the availability of required seats and fulfillment of any enrollment limits. If these conditions are not satisfied, the transaction should be rolled back, as accepting an invalid registration would violate the database's consistency.


Isolation ensures that concurrent transactions do not interfere with each other during execution. It safeguards against data inconsistencies that may arise due to concurrent access to the same data by multiple transactions. Each transaction must be isolated from others until it is completed. This property provides an illusion of executing transactions serially, even if they are running concurrently.

For example, if two users attempt to purchase the last remaining item of a product simultaneously, the isolation property ensures that only one transaction can access and claim the item, while the other transaction is delayed or rolled back.


Durability guarantees that once a transaction is committed and completed successfully, its effects persist, even in case of system failures or crashes. The changes made by the transaction are stored permanently and are not lost due to any subsequent system malfunction.

For example, if a customer places an order and the transaction is committed, the order should not disappear or be lost due to any failure, such as a power outage or system crash. The durability property ensures that the data is safely stored and can be retrieved whenever required, irrespective of any subsequent incidents.


Understanding the properties of transactions and their adherence to ACID principles is crucial for ensuring the reliability and integrity of databases. Atomicity guarantees the "all or none" execution of a transaction, while consistency ensures that transactions meet predefined rules and constraints. Isolation prevents interference among concurrent transactions, and durability ensures the permanent storage of committed transaction changes.

By implementing these ACID properties, database management systems maintain the integrity and consistency of data, leading to reliable and robust applications.

noob to master © copyleft