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Data & Analytics · Intermediate

Transaction Isolation Level

A setting that defines which concurrency anomalies a transaction may see: Read Uncommitted, Read Committed, Repeatable Read or Serializable.

Definition

Read Uncommitted allows dirty reads, Read Committed prevents them, Repeatable Read also prevents non-repeatable reads, and Serializable also prevents phantoms. Higher levels reduce concurrency. Snapshot isolation uses row versions to give a consistent view without read locks.

Example

SET TRANSACTION ISOLATION LEVEL REPEATABLE READ;

Exam tip

Memorize which anomaly each level prevents; that is the classic exam table.

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