Understanding How MySQL InnoDB Solves Phantom Reads
This article explains the four transaction isolation levels, defines phantom reads, and details how MySQL's InnoDB engine uses MVCC snapshot reads and next‑key locking (including the next‑key principle and lock composition) to prevent phantom reads under the REPEATABLE READ isolation level.
Transaction isolation in MySQL defines four levels—Read Uncommitted, Read Committed, Repeatable Read, and Serializable. This article focuses on how the InnoDB engine prevents phantom reads under the Repeatable Read level.
Details
A single diagram (shown below) illustrates the concept.
1. What is a phantom read?
2. Why must phantom reads be resolved?
3. How does MySQL solve phantom reads?
3.1 What is the next‑key principle?
3.2 What does a next‑key lock contain?
4. Does InnoDB’s RR isolation level eliminate phantom reads?
Conclusion
Phantom reads are clearly illustrated; to ensure high‑concurrency and data consistency, MySQL InnoDB uses MVCC snapshot reads together with next‑key (current) reads, and its default Repeatable Read isolation level effectively prevents phantom reads.
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