Concurrency anomalies
On This Lesson 4 topics
This lesson is planned. The outline below lists the topics it will cover. The full lesson has not been published yet.
In this lesson
name and recognize the five anomalies.
Planned topics
- Dirty read: reading another transaction's uncommitted data.
- Non-repeatable read: the same row read twice gives different values.
- Phantom: the same query returns a different set of rows the second time.
- Lost update: two transactions read, then both write; one overwrites the other.
- Write skew: two transactions read overlapping data and write different rows, breaking a rule that spans both (two doctors going off call).
Draft outline details
Demonstration
a timeline table for each anomaly with two columns (T1, T2) and the surprising result, using a Shop stock example for lost update.
Check your understanding
Two transactions each read stock = 5 and each write stock = 4. Which anomaly?
Show answer
Lost update.
Practice
Apply this lesson with the module's lab, exercises and quiz.
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