Classification and Application: Understand the types and uses of MySQL locks

Classification and application of MySQL locks

In order to ensure the consistency and integrity of the data in the case of concurrent access to the database, MySQL provides a lock mechanism. Locks can protect key resources and control access and modification of data by concurrent transactions. This article will introduce the classification and application of MySQL locks and provide specific code examples.

1. Classification of MySQL locks

MySQL locks can be divided into shared locks (Shared Lock) and exclusive locks (Exclusive Lock). Shared locks and exclusive locks are mutually exclusive and cannot exist on the same resource at the same time. Shared locks are used for read operations, allowing multiple transactions to acquire shared locks on the same resource at the same time; exclusive locks are used for write operations, allowing only one transaction to acquire an exclusive lock on a resource.

There are three types of locks commonly used in MySQL:

1. Table-level Locks: Table-level locks lock the entire table and can be divided into Read locks and write locks. Read locks are shared locks, and multiple transactions can acquire read locks at the same time; write locks are exclusive locks, and only one transaction can acquire write locks.
2. Row-level Locks: Row-level locks lock rows in the table. Only transactions that operate on a certain row will acquire the lock on that row. Row-level locks can accurately control data access by concurrent transactions, but the granularity of row-level locks is smaller, which increases the number and overhead of locks.
3. Page-level Locks: Page-level locks lock pages in the table. The size of each page is 16KB. Page-level locks are between table-level locks and row-level locks and can reduce the number and overhead of locks. However, the granularity control of page-level locks is poorer than that of row-level locks, which may lead to lock conflicts.

2. MySQL lock application

1. Table-level lock application example:

-- 事务1
START TRANSACTION;
LOCK TABLES table_name WRITE;
-- 执行写操作
COMMIT;

-- 事务2
START TRANSACTION;
LOCK TABLES table_name READ;
-- 执行读操作
COMMIT;

2. Row-level lock application example:

-- 事务1
START TRANSACTION;
SELECT * FROM table_name WHERE id = 1 LOCK IN SHARE MODE;
-- 读取数据
COMMIT;

-- 事务2
START TRANSACTION;
SELECT * FROM table_name WHERE id = 1 FOR UPDATE;
-- 更新数据
COMMIT;

3. Page-level lock application example:

-- 事务1
START TRANSACTION;
SELECT * FROM table_name WHERE id BETWEEN 1 AND 100 LOCK IN SHARE MODE;
-- 读取数据
COMMIT;

-- 事务2
START TRANSACTION;
SELECT * FROM table_name WHERE id BETWEEN 1 AND 100 FOR UPDATE;
-- 更新数据
COMMIT;

3. Summary

The classification and application of MySQL locks are an important component of database concurrency control part. Choosing an appropriate lock mechanism based on actual needs and using locks rationally can improve the concurrency performance and data consistency of the database. In actual applications, locks need to be selected and used according to specific scenarios to avoid deadlocks and performance problems.

I hope that the introduction of this article can help readers understand the classification and application of MySQL locks, and better understand the use of locks with specific code examples.

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