MySQL/InnoDB的并发插入Concurrent Insert

表people建表语句：ENGINE=InnoDB

CREATE TABLE people  (person_id BIGINT NOT NULL AUTO_INCREMENT,first_name VARCHAR(20),last_name VARCHAR(20),PRIMARY KEY (person_id)
);

两个会话：会话一和会话二

在会话一中，执行如下sql语句：

mysql> use local_database;
Database changed
mysql> select @@autocommit;
+--------------+
| @@autocommit |
+--------------+
|            1 |
+--------------+
1 row in set (0.00 sec)mysql> set autocommit = 0;
Query OK, 0 rows affected (0.00 sec)mysql> select @@autocommit;
+--------------+
| @@autocommit |
+--------------+
|            0 |
+--------------+
1 row in set (0.00 sec)mysql> select * from people;
+-----------+------------+-----------+
| person_id | first_name | last_name |
+-----------+------------+-----------+
|         1 | 1111       | 1111      |
+-----------+------------+-----------+
1 row in set (0.00 sec)mysql> begin;
Query OK, 0 rows affected (0.00 sec)mysql> insert into people (first_name,last_name) values ('1111','1111');
Query OK, 1 row affected (0.12 sec)mysql> select * from people;
+-----------+------------+-----------+
| person_id | first_name | last_name |
+-----------+------------+-----------+
|         1 | 1111       | 1111      |
|         3 | 1111       | 1111      |
+-----------+------------+-----------+
2 rows in set (0.00 sec)

上面这些sql 语句最终的操作就是手动开启了一个事务，然后提交了一个insert语句，注意没有手动提交事务。。

此时在另一个会话二中进行如下操作

mysql> use local_database;
Database changed
mysql> select @@autocommit;
+--------------+
| @@autocommit |
+--------------+
|            1 |
+--------------+
1 row in set (0.00 sec)mysql> set autocommit = 0;
Query OK, 0 rows affected (0.00 sec)mysql> select @@autocommit;
+--------------+
| @@autocommit |
+--------------+
|            0 |
+--------------+
1 row in set (0.00 sec)mysql> select * from people;
+-----------+------------+-----------+
| person_id | first_name | last_name |
+-----------+------------+-----------+
|         1 | 1111       | 1111      |
+-----------+------------+-----------+
1 row in set (0.00 sec)mysql> begin;
Query OK, 0 rows affected (0.00 sec)mysql> insert into people (first_name,last_name) values ('2222','2222');
Query OK, 1 row affected (0.00 sec)mysql> select * from people;
+-----------+------------+-----------+
| person_id | first_name | last_name |
+-----------+------------+-----------+
|         1 | 1111       | 1111      |
|         4 | 2222       | 2222      |
+-----------+------------+-----------+
2 rows in set (0.00 sec)

上面的sql语句最终的操作是手动开启了一个事务，执行了insert语句，而没有提交事务，然后select查看只会看到当前会话的操作结果，而没有会话一的操作结果。这就是mysql默认事务隔离级别——可重复读。

做到这里，我验证的不是可重复读的事务隔离级别，我其实想验证的是会话在事务内执行insert语句会不会给表加锁（会给表加锁，AUTO-INC lock），通过结果显示，可知，不同的会话在事务内执行insert语句，而不会阻塞其他会话事务内的insert语句。

但最终我产生了疑问，MySQL/InnoDB是如何处理并发插入的。

MySQL/InnoDB的并发插入

说起auto_increment的并发插入，就要理解auto_increment的机制了。见文章：

http://my.oschina.net/xinxingegeya/blog/341991

http://my.oschina.net/xinxingegeya/blog/342075

下面我写了两个程序测试并发插入，一个是单线程的写入10w条数据，一个是100条线程单个线程写入1000条数据。可以运行一下程序做一个对比。

建表语句

CREATE TABLE people_thread  (person_id BIGINT NOT NULL AUTO_INCREMENT,first_name VARCHAR(20),last_name VARCHAR(20),thread_name VARCHAR(20),PRIMARY KEY (person_id)
);

总之还是多线程的效率比较高：测试数据如下

单线程的运行时间为：-- 16656ms

多线程的最长的运行时间为：-- 12632ms

JDBCTest2.java

package com.lyx.other;import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;public class JDBCTest2 {public static void main(String args[]) throws SQLException {long startTime = System.currentTimeMillis(); // 获取开始时间Connection conn = null;PreparedStatement ps = null;String sql = "insert into people_thread (first_name ,last_name ,"+ "thread_name) values (?,?,?)";try {conn = getConnection();conn.setAutoCommit(false);ps = conn.prepareStatement(sql);for (int i = 0; i < 100000; i++) {ps.setString(1, Integer.toString(i));ps.setString(2, Integer.toString(i));ps.setString(3, Integer.toString(i));ps.addBatch();// 一批提交一次if (i % 10 == 0) {ps.executeBatch();ps.clearBatch();}}ps.executeBatch();conn.commit();} catch (Exception e) {// TODO: handle exceptione.printStackTrace();} finally {if (conn != null) {try {conn.close();} catch (SQLException e) {e.printStackTrace();}}}long endTime = System.currentTimeMillis(); // 获取结束时间System.out.println("程序运行时间： " + (endTime - startTime) + "ms");}/* 获取数据库连接的函数 */public static Connection getConnection() {Connection con = null; // 创建用于连接数据库的Connection对象try {Class.forName("com.mysql.jdbc.Driver");// 加载Mysql数据驱动con = DriverManager.getConnection("jdbc:mysql://localhost:3306/local_database", "root","034039");// 创建数据连接} catch (Exception e) {System.out.println("数据库连接失败" + e.getMessage());}return con; // 返回所建立的数据库连接}}

JDBCTest3.java

package com.lyx.other;import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;public class JDBCTest3 {public static void main(String[] args) {// 创建10个线程执行插入操作for (int i = 0; i < 100; i++) {final int n = i;Runnable task = new Runnable() {public void run() {Thread.currentThread().setName("thread_" + n);insertByBatch(Thread.currentThread().getName());}};Thread thread = new Thread(task);thread.start();}}public static void insertByBatch(String name) {long startTime = System.currentTimeMillis(); // 获取开始时间Connection conn = null;PreparedStatement ps = null;String sql = "insert into people_thread (first_name ,last_name ,"+ "thread_name) values (?,?,?)";try {conn = getConnection();conn.setAutoCommit(false);ps = conn.prepareStatement(sql);for (int i = 0; i < 1000; i++) {ps.setString(1, Integer.toString(i));ps.setString(2, Integer.toString(i));ps.setString(3, name);ps.addBatch();// 一批提交一次if (i % 10 == 0) {ps.executeBatch();ps.clearBatch();}}ps.executeBatch();conn.commit();} catch (Exception e) {// TODO: handle exceptione.printStackTrace();} finally {if (conn != null) {try {conn.close();} catch (SQLException e) {e.printStackTrace();}}}long endTime = System.currentTimeMillis(); // 获取结束时间System.out.println("程序运行时间： " + (endTime - startTime) + "ms");}/* 获取数据库连接的函数 */public static Connection getConnection() {Connection con = null; // 创建用于连接数据库的Connection对象try {Class.forName("com.mysql.jdbc.Driver");// 加载Mysql数据驱动con = DriverManager.getConnection("jdbc:mysql://localhost:3306/local_database", "root","034039");// 创建数据连接} catch (Exception e) {System.out.println("数据库连接失败" + e.getMessage());}return con; // 返回所建立的数据库连接}}

============END============