MySQL transaction isolation level and concurrency control

Title: An in-depth discussion of the isolation level and concurrency control of MySQL transactions

As database application scenarios become increasingly complex, the isolation level and concurrency control of transactions have become a key issue in database management an indispensable and important topic. As a widely used relational database management system, MySQL's transaction processing functions are also highly valued by developers. This article will deeply explore the isolation level and concurrency control of MySQL transactions, and analyze it with specific code examples.

1. MySQL transaction isolation level

MySQL supports four transaction isolation levels, namely READ UNCOMMITTED, READ COMMITTED, REPEATABLE READ and SERIALIZABLE. Different isolation levels have different effects on transaction concurrency control. Developers need to choose the appropriate isolation level based on actual needs.

1.1 READ UNCOMMITTED (read uncommitted)

READ UNCOMMITTED is the lowest isolation level, and transactions can read modifications made by other uncommitted transactions. Under this isolation level, there is the risk of dirty read (Dirty Read), that is, one transaction reads the data of another uncommitted transaction, which may cause data inconsistency.

-- 设置事务隔离级别为READ UNCOMMITTED
SET SESSION TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;

1.2 READ COMMITTED (read commit)

Under the READ COMMITTED isolation level, transactions can only read modifications made by other submitted transactions. This isolation level can avoid dirty reads, but there are still problems with non-repeatable reads and phantom reads.

-- 设置事务隔离级别为READ COMMITTED
SET SESSION TRANSACTION ISOLATION LEVEL READ COMMITTED;

1.3 REPEATABLE READ (repeatable read)

Under the REPEATABLE READ isolation level, the query results of a transaction will always remain consistent regardless of how other transactions modify the data during execution. This isolation level can avoid dirty reads and non-repeatable reads, but phantom reads may still occur.

-- 设置事务隔离级别为REPEATABLE READ
SET SESSION TRANSACTION ISOLATION LEVEL REPEATABLE READ;

1.4 SERIALIZABLE (Serialization)

SERIALIZABLE is the highest level of isolation level. Transactions will be executed in order and transactions are guaranteed not to affect each other. This isolation level can avoid dirty reads, non-repeatable reads, and phantom reads, but will reduce concurrency performance.

-- 设置事务隔离级别为SERIALIZABLE
SET SESSION TRANSACTION ISOLATION LEVEL SERIALIZABLE;

2. Concurrency control of MySQL transactions

In MySQL, in order to ensure that concurrent execution between transactions will not cause data inconsistency problems, concurrency control is required. Commonly used concurrency control methods include locking, MVCC (Multi-version Concurrency Control), etc.

2.1 Locking

MySQL supports different granularity locking mechanisms such as row-level locks and table-level locks. Developers can choose the appropriate locking method according to the actual situation. The following is an example of using row-level locks:

-- 开启事务
START TRANSACTION;

-- 使用行级锁
SELECT * FROM table_name WHERE id = 1 FOR UPDATE;

-- 执行更新操作
UPDATE table_name SET column_name = 'new_value' WHERE id = 1;

-- 提交事务
COMMIT;

2.2 MVCC

MVCC is a commonly used concurrency control method in MySQL, which achieves concurrent access by saving different versions of data. When reading data, it will not be affected by the modified version of the writing transaction, ensuring the consistency of the read operation. The following is an example of MVCC:

-- 开启事务
START TRANSACTION;

-- 执行查询操作
SELECT * FROM table_name WHERE id = 1;

-- 提交事务
COMMIT;

Conclusion

The isolation level and concurrency control of MySQL transactions are important aspects that cannot be ignored in database management. Correctly configuring the isolation level and concurrency control methods can improve Database stability and performance. Through the introduction and examples of this article, I believe that readers will have a deeper understanding of the isolation level and concurrency control of MySQL transactions, and can better apply it in actual projects.

The above is an introduction to the isolation level and concurrency control of MySQL transactions. I hope it will be helpful to readers.

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