What are transaction isolation levels?
Model answer
They define what one transaction can see of another's changes: Read Uncommitted, Read Committed (default in PostgreSQL), Repeatable Read (default in MySQL InnoDB) and Serializable. Higher levels prevent more anomalies (dirty reads, non-repeatable reads, phantom reads) but allow less concurrency.
Learn this topic
Indexes and Faster Queries: EXPLAIN for Beginners in the course SQL for Beginners: Learn Databases Step by Step.
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