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Write Skew Under Read Committed

Run the Write Skew MicroSim Fullscreen

About This MicroSim

A canonical write-skew anomaly. Two concurrent transactions both check the rule "≥1 doctor must remain on call," each sees that the rule is satisfied, and each releases a different doctor. Under Read Committed, both commit; the result is zero doctors on call. Switch to Serializable isolation and replay: one transaction is aborted and retried, and the rule holds.

Lesson Plan

Learning Objectives

By the end of this activity, students will be able to:

  1. Trace two concurrent transactions through a write-skew scenario
  2. Identify why Read Committed allows the anomaly
  3. Explain how Serializable prevents it at the cost of one rollback