ACID

Definition

ACID is an acronym for Atomicity, Consistency, Isolation, and Durability. These four properties define the reliability of transactions in relational database systems. A transaction is a sequence of operations that must be completed successfully as a single unit of work to ensure data integrity.

ACID compliance guarantees that even in cases of errors, power failures, or crashes, the database remains accurate and reliable. This makes ACID critical for applications that handle financial transactions, order management, and other mission-critical data.

Advanced

Atomicity ensures that all parts of a transaction succeed or none are applied. Consistency maintains the validity of data according to defined rules and constraints. Isolation ensures that concurrent transactions do not interfere with each other. Durability guarantees that once a transaction is committed, it will persist even in the event of a system failure.

Advanced relational databases implement ACID using techniques such as transaction logs, locking mechanisms, and write-ahead logging. These features provide strong guarantees but can reduce performance compared to eventual consistency models in some NoSQL databases.

Why it matters

• Protects data integrity in mission-critical systems.
• Ensures reliable transactions for financial and operational processes.
• Reduces risks of data corruption during concurrent operations.
• Provides predictable behaviour for complex database interactions.

Use cases

• Banking systems that process deposits and withdrawals.
• E-commerce platforms managing customer orders and payments.
• Enterprise resource planning systems tracking inventory and logistics.
• Healthcare applications storing patient records securely.

Metrics

• Transaction success and failure rates.
• Latency of transaction processing.
• Recovery time after system crashes.
• Consistency checks across multiple operations.

Issues

• Performance overhead due to locking and logging mechanisms.
• Limited scalability for massive distributed systems.
• Complexity in managing high volumes of concurrent transactions.
• May not suit applications that prioritise speed over strict consistency.

Example

A bank uses an ACID-compliant SQL database to handle fund transfers. If a customer initiates a transfer, atomicity ensures both the debit and credit occur together. Even if the system crashes during the process, durability guarantees that once committed, the transaction remains permanent.