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Explain database transactions and ACID

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MediumSoftware EngineerTechnical ScreenSystem Design

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This question evaluates a candidate's understanding of database transactions including ACID properties, isolation levels (read uncommitted, read committed, repeatable read, serializable), common anomalies (dirty reads, non-repeatable reads, phantom reads), MVCC, and commit/rollback semantics, testing competency in transactional correctness and concurrency control. Commonly asked in System Design and database contexts because it probes reasoning about data integrity, visibility, and durability under concurrent workloads, and it tests both conceptual understanding of transactional guarantees and practical application of isolation behavior in relational database systems.

Explain database transactions and ACID. Define atomicity, consistency, isolation, and durability; compare common isolation levels (read uncommitted, read committed, repeatable read, serializable) and the anomalies they prevent (dirty reads, non-repeatable reads, phantom reads). Describe how commits and rollbacks work, how MVCC helps achieve isolation, and outline an example schema and sequence of statements that demonstrate correct use of a transaction under concurrency.