ACID

ACID is an acronym that represents a set of properties that ensure the reliability and integrity of transactions in a database management system. These properties are fundamental for maintaining data consistency and ensuring that the database remains in a valid state, even in the presence of failures or concurrent access by multiple users. ACID stands for:

1. Atomicity: Atomicity ensures that a transaction is treated as a single, indivisible unit of work. It guarantees that either all the operations within a transaction are completed successfully, or none of them are. In case of a failure (such as a system crash or error), any changes made by an incomplete transaction are rolled back, leaving the database in a consistent state.
2. Consistency: Consistency ensures that a transaction brings the database from one consistent state to another. This means that a transaction’s operations must adhere to any predefined rules or constraints, maintaining the overall integrity of the database. If a transaction violates these rules, the database remains unchanged, and the transaction is not committed.
3. Isolation: Isolation ensures that multiple transactions can be executed concurrently without interfering with each other. Each transaction is isolated from the others until it is completed (either committed or rolled back). This prevents transactions from seeing intermediate states of other transactions and helps avoid issues like “dirty reads,” “phantom reads,” and “non-repeatable reads.”
4. Durability: Durability ensures that once a transaction is committed, its changes are permanent and will survive any subsequent system failures, such as crashes or power outages. Committed changes are stored in non-volatile storage (such as disk drives) to ensure they are available even if the system restarts.

ACID properties are crucial for maintaining data integrity and reliability in database systems, especially in environments where multiple users or applications access and modify the same data simultaneously. These properties ensure that transactions are executed correctly, even in the presence of hardware or software failures, and that the database remains in a consistent and valid state at all times. However, it’s important to note that enforcing strict ACID properties can sometimes impact performance and scalability, leading to trade-offs in certain high-concurrency or distributed systems. In such cases, alternative consistency models like BASE (Basically Available, Soft state, Eventually consistent) may be considered.