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Explain ACID and isolation levels

MetaSoftware Engineer · Onsite
MediumSoftware EngineerOnsiteSoftware Engineering Fundamentals

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This question evaluates a candidate's knowledge of database transactions, the ACID properties (Atomicity, Consistency, Isolation, Durability), and common isolation levels (Read Uncommitted, Read Committed, Repeatable Read, Serializable), testing competency in concurrency control and data consistency.

Explain what a database transaction is, define the ACID properties (Atomicity, Consistency, Isolation, Durability), and describe common transaction isolation levels: Read Uncommitted, Read Committed, Repeatable Read, and Serializable.

For each isolation level, discuss:

  • Which anomalies it prevents or allows (e.g., dirty reads, non-repeatable reads, phantom reads).
  • A concrete example scenario illustrating those anomalies.
  • When you might choose that level in a real-world application (e.g., financial system vs. analytics system).

Also explain how isolation relates to performance and concurrency in a database system.