Tan Chia ChunACID Principles
An explanation of the ACID properties (Atomicity, Consistency, Isolation, and Durability), that ensure reliable database transactions.
Introduction
Ever wondered how databases manage to keep your data accurate and consistent even when multiple users are interacting with them at the same time? The answer lies in the ACID properties.
ACID is an acronym that stands for:
- Atomicity
- Consistency
- Isolation
- Durability
These properties are essential to ensure reliable and robust database transactions.
Atomicity
Atomicity means that a transaction is an all-or-nothing operation. Either all the operations within the transaction are completed successfully, or none are.
Example:
If you’re transferring money between two accounts:
- Deduct from Account A
- Add to Account B
If step 2 fails, step 1 must be rolled back to maintain balance integrity.
Consistency
Consistency ensures that a transaction brings the database from one valid state to another, maintaining all predefined rules, such as constraints, cascades, and triggers.
Example:
If there's a rule that a user’s age must be >= 0, any transaction that tries to insert -5 as an age will be rejected to maintain consistency.
Isolation
Isolation means that the operations of one transaction are invisible to other transactions until the transaction is complete. This prevents concurrent transactions from interfering with each other.
Example:
Two people trying to book the last ticket at the same time. Isolation ensures only one succeeds.
Databases implement isolation through various isolation levels (Read Uncommitted, Read Committed, Repeatable Read, Serializable).
Durability
Durability guarantees that once a transaction is committed, its changes are permanent, even in the case of a power failure or crash.
Example:
Once your online purchase confirms your order, that transaction is saved to disk and will not be lost, even if the server crashes right after.
Why ACID Matters
Without ACID properties:
- Data might become inconsistent or incorrect
- Users might see stale or incorrect information
- Systems may be vulnerable to crashes and data loss
In short, ACID is what makes transactional databases trustworthy.
Final Thoughts
Understanding ACID helps you reason about how your applications handle data and avoid bugs, corruption, and concurrency issues.
If your project requires high data integrity (e.g., banking, healthcare, ecommerce), always make sure your database supports and adheres to ACID principles.