How to use MySQL's transaction isolation level to deal with concurrent transaction issues

How to use MySQL's transaction isolation level to handle concurrent transaction issues

1. Introduction

When using MySQL for concurrent transaction processing, you may encounter some problems, such as Data inconsistency, dirty reads, phantom reads, etc. In order to solve these problems, MySQL provides the function of transaction isolation level, which can handle concurrent transactions by setting different isolation levels.

In this article, we will introduce MySQL’s four transaction isolation levels and demonstrate through sample code how to use these isolation levels to handle concurrent transaction issues.

2. MySQL’s transaction isolation level

MySQL’s four transaction isolation levels are: Read Uncommitted, Read Committed, and Can Repeatable Read and Serializable.

• Read uncommitted: The lowest isolation level, transactions can read uncommitted data, which may cause dirty read problems.
• Read Committed: Transactions can only read submitted data, avoiding dirty read problems, but non-repeatable read problems may occur.
• Repeatable reading: Ensure that the results of multiple reads of the same data in the same transaction are consistent, avoiding the problem of non-repeatable reading, but phantom reading problems may occur.
• Serialization: The highest isolation level, transactions will be executed completely serially, avoiding phantom read problems, but it will lead to reduced concurrency performance.

3. Example of using transaction isolation level

Below we use sample code to demonstrate how to use MySQL's transaction isolation level to handle concurrent transaction issues.

import pymysql

# 连接数据库
conn = pymysql.connect(host='localhost', port=3306, user='root', password='密码', db='test')

# 创建游标
cursor = conn.cursor()

# 设置事务隔离级别为读已提交
cursor.execute('SET TRANSACTION ISOLATION LEVEL READ COMMITTED')

# 开始事务
cursor.execute('START TRANSACTION')

try:
    # 执行SQL语句
    cursor.execute('UPDATE users SET balance = balance - 100 WHERE id = 1')
    cursor.execute('UPDATE users SET balance = balance + 100 WHERE id = 2')

    # 提交事务
    conn.commit()
except Exception as e:
    # 回滚事务
    conn.rollback()
    print('事务执行失败:', str(e))

# 关闭游标和连接
cursor.close()
conn.close()

In the above example code, we first created a MySQL connection and set the transaction isolation level to read committed. Then, we started a transaction and executed two SQL statements, subtracting 100 from user 1's balance and adding 100 to user 2's balance. Finally, the results of transaction execution are processed by committing the transaction or rolling back the transaction.

4. Summary

In this article, we introduced the four transaction isolation levels of MySQL and demonstrated how to use these isolation levels to deal with concurrent transaction issues through sample code . I hope this article will help you understand MySQL's transaction isolation level and deal with concurrent transaction issues.

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