Explain ACID and isolation levels

Describe what a database transaction is, define the ACID properties—Atomicity, Consistency, Isolation, Durability—and explain the standard transaction isolation levels: Read Uncommitted, Read Committed, Repeatable Read, and Serializable.

For each isolation level, cover:

• Which anomalies it blocks or permits, such as dirty reads, non-repeatable reads, and phantom reads.
• A specific example scenario that shows those anomalies.
• When you would pick that level in a practical application, for instance a financial system versus an analytics system.

Also explain the connection between isolation and database performance and concurrency.

Overview: This question assesses a candidate's understanding of database transactions, the ACID properties—Atomicity, Consistency, Isolation, Durability—and the common isolation levels—Read Uncommitted, Read Committed, Repeatable Read, Serializable—while testing skill in concurrency control and data consistency.