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  "description": "ACID is the set of guarantees a database transaction provides: Atomicity, Consistency, Isolation, Durability. ACID is the bedrock contract that makes relational databases trustworthy for financial, inventory, identity, and other workloads where partial or inconsistent state is unacceptable.\n\n\nWhat each letter means\n\n * Atomicity. A transaction either completes entirely or has no effect. There is no halfway state visible to anyone else.\n * Consistency. A transaction takes the database from one va",
  "path": "/engineering-glossary/acid-database-transactions/",
  "publishedAt": "2026-05-12T18:46:29.000Z",
  "site": "https://sahilkapoor.com",
  "tags": [
    "SQL",
    "PostgreSQL",
    "MVCC",
    "OLTP",
    "Eventual Consistency"
  ],
  "textContent": "**ACID** is the set of guarantees a database transaction provides: Atomicity, Consistency, Isolation, Durability. ACID is the bedrock contract that makes relational databases trustworthy for financial, inventory, identity, and other workloads where partial or inconsistent state is unacceptable.\n\n## What each letter means\n\n  * **Atomicity.** A transaction either completes entirely or has no effect. There is no halfway state visible to anyone else.\n  * **Consistency.** A transaction takes the database from one valid state to another, respecting all declared constraints (foreign keys, uniqueness, check constraints).\n  * **Isolation.** Concurrent transactions do not interfere with each other. Different isolation levels offer different tradeoffs between concurrency and anomalies.\n  * **Durability.** Once a transaction commits, its effects survive crashes, power loss, and restarts.\n\n\n\n## Isolation levels\n\nSQL defines four standard levels from weakest to strongest:\n\n  * **Read Uncommitted.** Sees others' uncommitted changes (dirty reads).\n  * **Read Committed.** Sees only committed data, but the same query can return different results in a transaction (non-repeatable reads).\n  * **Repeatable Read.** Stable reads within a transaction; phantom rows may still appear.\n  * **Serializable.** Behaves as if transactions ran one at a time.\n\n\n\nMost databases default to Read Committed; some (PostgreSQL with serializable, CockroachDB) provide stronger guarantees via MVCC and serializable snapshot isolation.\n\n🔗\n\n**Related Terms**\nSQL, PostgreSQL, MVCC, OLTP, Eventual Consistency.",
  "title": "ACID",
  "updatedAt": "2026-05-13T19:14:39.244Z"
}