What ACID is
ACID is a set of four properties that help guarantee that database transactions are processed reliably. The letters stand for atomicity, consistency, isolation, and durability. Together, these properties describe the qualities a transaction should have so that data remains correct even in the face of errors, interruptions, or many transactions happening at once. A transaction is a unit of work, such as a group of related changes, that should be treated as a whole. ACID is a foundational idea in reliable databases, setting the expectations that make them trustworthy for important data.
Atomicity
Atomicity means that a transaction is treated as a single, indivisible unit: either all of its parts happen, or none of them do. If a transaction involves several steps and something goes wrong partway through, atomicity ensures the whole transaction is undone rather than left half-complete. This prevents partial changes from corrupting the data, keeping operations all-or-nothing.
Consistency
Consistency means that a transaction brings the database from one valid state to another, preserving the rules and constraints that keep the data correct. A transaction should not leave the database in a state that violates its defined rules. By enforcing consistency, the database ensures that completed transactions keep the data valid and meaningful according to the structure that governs it.
Isolation
Isolation concerns how transactions behave when running at the same time. It ensures that concurrently executing transactions do not interfere with one another in ways that would produce incorrect results. With proper isolation, each transaction can proceed as though it were operating on its own, even when many are running together, which protects the correctness of the data.
Durability
Durability means that once a transaction has been completed and committed, its changes are permanent, even if the system subsequently fails. The results are safely recorded so they are not lost by a crash or power loss. Durability gives confidence that a successful transaction's effects will persist, which is essential for trusting a database with important data.
Why it matters
ACID is a fundamental concept behind reliable databases. Understanding what ACID is - atomicity, consistency, isolation, and durability - clarifies how databases keep data correct and safe through transactions. For anyone working with databases, it is a valuable concept to understand.
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See also: What is a transaction in databases? Explained, What are database isolation levels? Explained.
Sources
Published date reflects the original event date (2025-10-28). This article is original Skillo editorial written from the sources above; facts were verified in September 2026.
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