In transaction management, which ACID property means that once a transaction commits, all of its changes are permanent and will survive subsequent system failures?

Introduction / Context:
Database transactions are governed by the ACID properties: atomicity, consistency, isolation, and durability. These properties ensure that transactions behave reliably even in the presence of errors, concurrency, and system failures. This question focuses on the property that guarantees that once a transaction has been committed, its effects remain in the database and are not lost, even if the system crashes shortly afterward.

Given Data / Assumptions:

We are working with a transactional database system that implements the ACID properties.
A transaction is a logical unit of work that may involve several read and write operations.
Commit marks the successful completion of a transaction, while rollback undoes its changes.
We want the system to guarantee that committed changes are not lost due to power failures or crashes.
The four ACID properties are assumed to have their standard textbook meanings.

Concept / Approach:
Atomicity means that a transaction is all or nothing: either all operations take effect or none do. Consistency means that a transaction moves the database from one valid state to another, preserving all constraints. Isolation means that concurrent transactions behave as if they were executed one after another in some serial order, with no interference. Durability is the property that ensures that once a transaction commits, its changes are recorded in non volatile storage and will persist across system failures. The question clearly describes permanent committed changes, which is the domain of durability.

Step-by-Step Solution:
Step 1: Identify the property described in the question. It states that once a transaction commits, all of its changes are permanent. Step 2: Recall the definitions of the four ACID properties and match the description to the correct one. Atomicity is about all or nothing, consistency is about valid states, isolation is about concurrent behaviour, and durability is about permanence of committed changes. Step 3: Recognize that durability is the property that deals with permanent storage of committed transactions, often implemented using logs and recovery mechanisms. Step 4: Choose durability as the correct answer.

Verification / Alternative check:
Consider what happens during a system crash immediately after a transaction commits. A durable system uses a transaction log and write ahead logging so that all changes can be reconstructed during recovery. If the system can restore all committed changes and does not roll them back, then durability is satisfied. If instead a committed transaction could be partially lost, then durability would be violated. This example confirms that the property described in the question is durability rather than atomicity, consistency, or isolation.

Why Other Options Are Wrong:
Atomic means that a transaction either fully completes or has no effect, but it does not itself guarantee that changes persist after a crash. It works together with durability but is a different concept.
Consistent means that transactions respect all defined constraints, such as referential integrity, but it says nothing about what happens after system failures.
Isolated means that concurrent transactions do not interfere with each other, so they appear to run one after another. Again, this is not about permanent storage of committed changes.

Common Pitfalls:
A frequent confusion is to mix up atomicity and durability, because both deal with the idea of reliability. Another pitfall is to assume that if a transaction commits, then the application does not need to consider the possibility of later failures. In reality, durability is implemented by careful logging and recovery algorithms, and misconfigurations at the storage level can still cause data loss. Understanding the distinct role of durability helps developers appreciate why proper backup, logging, and hardware configuration are critical.

Final Answer:
The ACID property that ensures committed changes are permanent is durability.