MySQL Repeatable Read: MVCC Implementation for Consistent Reads

MySQL's Repeatable Read isolation level utilizes MVCC (Multi-Version Concurrency Control) to implement repeatable reads. MVCC is a concurrency control mechanism that creates a snapshot of the database at the start of each transaction. This snapshot is used during the transaction to ensure repeatable reads. In MVCC, each transaction has its own read version, determined at the transaction's initiation. When a transaction reads data, it only sees data committed before its start, not data from uncommitted transactions. This guarantees consistent data for the transaction, unaffected by concurrent transactions. The benefit of using MVCC for repeatable reads is reduced lock usage, enhancing concurrency performance. MVCC allows read operations to proceed without blocking write operations or other read operations. Conflicts arise only between write operations, necessitating lock mechanisms for data consistency. Under the Repeatable Read isolation level, reads exclusively utilize MVCC, not locks.