An in-depth discussion of the locking mechanism of the MySQL InnoDB engine

In-depth analysis of MySQL InnoDB locks

In the MySQL database, locks are an important mechanism to ensure data integrity and consistency. As one of the most commonly used storage engines in MySQL, the InnoDB storage engine has attracted much attention for its locking mechanism. This article will provide an in-depth analysis of the locking mechanism of the InnoDB storage engine, including lock types, locking rules, deadlock handling, etc., and provide specific code examples to help readers better understand.

1. Types of locks

In the InnoDB storage engine, locks are mainly divided into two types: shared locks (S locks) and exclusive locks (X locks). Shared locks are used for read operations and can be held by multiple transactions and are not mutually exclusive; exclusive locks are used for write operations and can only be held by one transaction and are mutually exclusive with other locks. In addition, InnoDB also supports row-level locking, which locks data rows instead of the entire table, which greatly improves concurrency performance.

2. Locking rules

The InnoDB storage engine follows strict locking rules, which mainly include the following points:

1. When a transaction reads data , a shared lock will be added to the data row, preventing other transactions from modifying the data row, but not preventing other transactions from reading the data row.
2. When a transaction writes data, it will add an exclusive lock to the data row to prevent other transactions from reading and writing the data row.
3. When a transaction holds a shared lock on a data row, other transactions can hold a shared lock on the data row at the same time, but cannot hold an exclusive lock; when a transaction holds an exclusive lock on a data row, Then other transactions cannot hold shared locks and exclusive locks.
4. The InnoDB storage engine uses multi-version concurrency control (MVCC) to achieve concurrency in read and write operations. It can not only achieve separation of read and write, but also reduce lock conflicts and improve concurrency performance.

3. Deadlock handling

In a concurrent environment, deadlock situations will inevitably occur because the interaction between transactions is complex. When two or more transactions A deadlock occurs when each party waits for the lock held by the other party. The InnoDB storage engine adopts a timeout rollback policy for deadlocks. That is, when a deadlock occurs, the system will detect the deadlock and roll back transactions holding fewer locks to break the deadlock and ensure the normal operation of the system.

4. Code Example

Next, we use a specific code example to demonstrate the locking mechanism of the InnoDB storage engine. Suppose we have a table named employee, which contains three fields: id, name and salary. Here is a simple example Code:

-- 开启事务
START TRANSACTION;

-- 事务1：对id为1的员工进行读操作
SELECT * FROM employee WHERE id = 1 FOR SHARE;

-- 事务2：对id为1的员工进行写操作
UPDATE employee SET salary = 6000 WHERE id = 1;

-- 提交事务
COMMIT;

In the above example, transaction 1 first performs a read operation on the shared lock on the employee with id 1, while transaction 2 attempts to perform an exclusive lock write operation on the same data row. Since transaction 1 holds the shared lock, transaction 2 cannot obtain the exclusive lock and will be blocked until transaction 1 releases the lock. This example clearly demonstrates the locking mechanism and locking rules of the InnoDB storage engine.

5. Summary

Through the in-depth analysis of this article, we have learned about the locking mechanism of the InnoDB storage engine, including lock types, locking rules, deadlock processing, etc., and through specific Code examples are demonstrated. In actual development, rational use of InnoDB's locking mechanism is crucial to ensuring the concurrency performance and data consistency of the system. I hope that this article will give readers a clearer understanding of the locking mechanism of InnoDB storage engine.

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