Lock strategy in MySQL concurrency control

MySQL lock concurrency control strategy

Introduction:
In the database system, in order to ensure the consistency and integrity of the data, concurrent operations need to be controlled . The lock mechanism is a commonly used concurrency control strategy. As a commonly used relational database management system, MySQL also has its own lock mechanism. Let's learn more about the concurrency control strategy of MySQL locks and provide specific code examples.

1. Overview of MySQL locks:
MySQL provides multiple types of locks, the commonly used ones are row locks (Record Locks), table locks (Table Locks) and optimistic locks (Optimistic Locks).
Row lock is the default locking mechanism of MySQL. When a row data needs to be updated or deleted in a transaction, the row data will be locked. When other transactions need to operate on this row of data, they must wait for the lock to be released.
Table lock is MySQL's lower-level locking mechanism. It locks the entire table. When a transaction operates on the table, other transactions cannot perform any operations on the table, even if these operations do not conflict.
Optimistic locking is a concurrency control strategy that has nothing to do with the locking mechanism in the database. It avoids the problem of dirty writes by checking whether the data has been modified by other transactions before performing write operations.

2. MySQL row lock:
The row lock in MySQL is a fine-grained lock control. It only locks the rows that need to be modified, not the entire table. The implementation of row lock is based on the two-phase lock protocol, that is: when the transaction starts, the row that needs to be modified is locked; when the transaction is committed, the lock is released.
The following is a specific example code for using row locks:

-- 创建测试表
CREATE TABLE test (
    id INT PRIMARY KEY,
    value INT
);

-- 开启事务
START TRANSACTION;

-- 查询并锁定行
SELECT * FROM test WHERE id = 1 FOR UPDATE;

-- 修改行数据
UPDATE test SET value = 10 WHERE id = 1;

-- 提交事务
COMMIT;

3. MySQL table lock:
When you need to operate the entire table, you can use table locks for concurrency control. Table lock is a coarser-grained lock control that locks the entire table rather than row data. Using table locks will cause significant blocking to other transactions, so table locks should be used with caution in actual applications.
The following is a specific example code for using table locks:

-- 创建测试表
CREATE TABLE test (
    id INT PRIMARY KEY,
    value INT
);

-- 开启事务
START TRANSACTION;

-- 锁定表
LOCK TABLES test WRITE;

-- 修改表数据
UPDATE test SET value = 10;

-- 解锁表
UNLOCK TABLES;

-- 提交事务
COMMIT;

4. MySQL optimistic locking:
The optimistic locking in MySQL is a concurrency control strategy implemented through version numbers. Each data row has a version number. When a transaction reads data, it will save the current version number and check whether its version number has been modified by other transactions before committing. If the version numbers are the same, you can commit; if the version numbers are different, it means that the data has been modified by other transactions, and you need to roll back and re-read before trying the operation again.
The following is a specific example code using optimistic locking:

-- 创建测试表
CREATE TABLE test (
    id INT PRIMARY KEY,
    value INT,
    version INT
);

-- 开启事务
START TRANSACTION;

-- 查询并获取当前版本号
SELECT version INTO @old_version FROM test WHERE id = 1;

-- 更新数据
UPDATE test SET value = 10, version = version + 1 WHERE id = 1 AND version = @old_version;

-- 检查更新结果
IF ROW_COUNT() = 1 THEN
    COMMIT;
ELSE
    ROLLBACK;
END IF;

Conclusion:
MySQL provides a variety of lock mechanisms to achieve concurrency control, of which row locks are the most commonly used lock type. When using the lock mechanism, it is necessary to select an appropriate lock mechanism according to the specific application scenario to improve the efficiency and correctness of concurrent data operations.

Reference materials:

1. MySQL Documentation: https://dev.mysql.com/doc/
2. MySQL Tutorial: https://www.mysqltutorial. org/
3. MySQL lock implementation: row lock and table lock: https://mp.weixin.qq.com/s/RLt1LpEBSOsGn7opxSopBA
4. MySQL optimistic lock implementation and usage scenario analysis ：https://blog.csdn.net/qq_38229163/article/details/80452138

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