How to implement MySQL underlying optimization: transaction concurrency control and isolation level selection

How to implement MySQL underlying optimization: transaction concurrency control and isolation level selection

Summary:
In the MySQL database, transaction concurrency control and isolation level selection Selection is important for database performance and data consistency. This article will introduce how to implement concurrency control and isolation level selection of MySQL transactions through underlying optimization, and provide specific code examples.

1. Transaction concurrency control
Transaction concurrency control refers to ensuring data consistency and concurrency when multiple transactions access the database at the same time. In MySQL, commonly used concurrency control methods include Two-Phase Locking (2PL), Multi-Version Concurrency Control (MVCC) and Optimistic Concurrency Control (OCC).

1. Two-phase locking (2PL)
   Two-phase locking is one of the more commonly used concurrency control methods. Locks are used to control concurrency when transactions perform read and write operations. The following is a sample code that uses 2PL to implement concurrency control:

START TRANSACTION;  -- 开启事务

-- 对数据表加锁
LOCK TABLES table1 WRITE, table2 READ;

-- 执行具体的读写操作，如：
SELECT * FROM table1 WHERE id = 1;
UPDATE table1 SET column1 = 'value1' WHERE id = 1;

-- 释放锁定
UNLOCK TABLES;

COMMIT; -- 提交事务

2. Multi-version concurrency control (MVCC)
   Multi-version concurrency control uses version numbers to achieve concurrent access to data. Each transaction reads a snapshot of the database at the time it was started. The following is a sample code that uses MVCC to implement concurrency control:

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

START TRANSACTION;  -- 开启事务

-- 执行具体的读写操作，如：
SELECT * FROM table1 WHERE id = 1;
UPDATE table1 SET column1 = 'value1' WHERE id = 1;

COMMIT; -- 提交事务

3. Optimistic Concurrency Control (OCC)
   Optimistic concurrency control does not use locks, but does conflict detection when the transaction is committed. . The following is a sample code that uses OCC to implement concurrency control:

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

START TRANSACTION;  -- 开启事务

-- 执行具体的读写操作，如：
SELECT * FROM table1 WHERE id = 1;
UPDATE table1 SET column1 = 'value1' WHERE id = 1;

COMMIT; -- 提交事务

2. Isolation level selection
The isolation level of a transaction determines the visibility between transactions and the degree of concurrency control. MySQL provides four isolation levels: READ UNCOMMITTED (read uncommitted), READ COMMITTED (read committed), REPEATABLE READ (repeatable read) and SERIALIZABLE (serialization).

In MySQL, the default isolation level is REPEATABLE READ. Here is sample code on how to select different isolation levels:

1. READ UNCOMMITTED

SET SESSION TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;

START TRANSACTION;

-- 执行具体的读写操作

COMMIT;

2. READ COMMITTED

SET SESSION TRANSACTION ISOLATION LEVEL READ COMMITTED;

START TRANSACTION;

-- 执行具体的读写操作

COMMIT;

3. REPEATABLE READ

SET SESSION TRANSACTION ISOLATION LEVEL REPEATABLE READ;

START TRANSACTION;

-- 执行具体的读写操作

COMMIT;

4. SERIALIZABLE

SET SESSION TRANSACTION ISOLATION LEVEL SERIALIZABLE;

START TRANSACTION;

-- 执行具体的读写操作

COMMIT;

Conclusion:
By optimizing transaction concurrency control and isolation level selection, the performance and data of the MySQL database can be improved consistency. In actual applications, appropriate concurrency control methods and isolation levels need to be selected based on specific business requirements and database load conditions.

It is worth noting that during the actual development process, in addition to the concurrency control and isolation level selection at the bottom of the database, you also need to pay attention to the design of database indexes, optimization of query statements, etc., to further improve the performance of the database. and response speed.

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