随着MySQL的应用日益广泛，支持事务特性的InnoDB已经成为MySQL的默认存储引擎。和很多关系数据库不同的是，在
InnoDB存储引擎中，事务默认是自动提交的，也就是说每条DML语句都会触发commit操作。这一自动提交(autocommit)特性在很多场景下对于性能还是有一定影响的。
最近我们尝试将一个Oracle数据库的数据迁移到MySQL数据库，发现导入时间很长。举个例子来说，其中有一个表包含四千多条数据，插入时间竟然超过了100秒。每插入一条数据，数据库就会自动提交一次，也就是说单这一个表MySQL会commit超过4000次，如果我们关闭自动提交功能，通过程序来控制，只要一次commit就可以了。
那么，如何关闭MySQL的autocommit特性呢？
通常有两种方法：
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一种是通过set命令修改会话级别或者数据库级别的参数，但是数据库重启后参数会恢复默认值；
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第二种方法是修改mysql的配置文件my.ini，一劳永逸。
1.测试环境 Windows Server 2008 r2+MySQL Community Server (GPL) 5.7.16
我是在Windows Server 2008 r2环境下进行测试。
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mysql> status
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--------------
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mysql Ver 14.14 Distrib 5.7.16, for Win64 (x86_64)
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Connection id: 2
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Current database:
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Current user: root@localhost
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SSL: Not in use
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Using delimiter: ;
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Server version: 5.7.16 MySQL Community Server (GPL)
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Protocol version: 10
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Connection: localhost via TCP/IP
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Server characterset: latin1
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Db characterset: latin1
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Client characterset: utf8
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Conn. characterset: utf8
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TCP port: 3306
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Uptime: 9 min 5 sec
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Threads: 1 Questions: 7 Slow queries: 0 Opens: 106 Flush tables: 1 Open tables: 99 Queries per second avg: 0.012
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--------------
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mysql>
2.通过set来关闭autocommit，重启后恢复默认值
首先，我们通过set命令来修改autocommit参数。
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mysql>
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mysql> show global variables like '%commit%';
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+-----------------------------------------+-------+
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| Variable_name | Value |
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+-----------------------------------------+-------+
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| autocommit | ON |
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| binlog_group_commit_sync_delay | 0 |
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| binlog_group_commit_sync_no_delay_count | 0 |
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| binlog_order_commits | ON |
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| innodb_api_bk_commit_interval | 5 |
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| innodb_commit_concurrency | 0 |
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| innodb_flush_log_at_trx_commit | 1 |
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| slave_preserve_commit_order | OFF |
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+-----------------------------------------+-------+
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8 rows in set, 1 warning (0.00 sec)
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mysql> set autocommit=0;
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Query OK, 0 rows affected (0.00 sec)
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mysql>
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mysql> set global autocommit=0;
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Query OK, 0 rows affected (0.00 sec)
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mysql> show global variables like '%commit%';
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+-----------------------------------------+-------+
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| Variable_name | Value |
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+-----------------------------------------+-------+
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| autocommit | OFF |
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| binlog_group_commit_sync_delay | 0 |
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| binlog_group_commit_sync_no_delay_count | 0 |
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| binlog_order_commits | ON |
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| innodb_api_bk_commit_interval | 5 |
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| innodb_commit_concurrency | 0 |
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| innodb_flush_log_at_trx_commit | 1 |
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| slave_preserve_commit_order | OFF |
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+-----------------------------------------+-------+
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8 rows in set, 1 warning (0.02 sec)
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mysql>
接下来，我们重启数据库，发现autocommit参数已经恢复默认值。
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E:\mysql-5.7.16-winx64\bin>net stop mysql
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MySQL 服务正在停止.
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MySQL 服务已成功停止。
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E:\mysql-5.7.16-winx64\bin>net start mysql
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MySQL 服务正在启动 .
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MySQL 服务已经启动成功。
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E:\mysql-5.7.16-winx64\bin>mysql -u root -proot
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mysql: [Warning] Using a password on the command line interface can be insecure.
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Welcome to the MySQL monitor. Commands end with ; or \g.
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Your MySQL connection id is 2
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Server version: 5.7.16 MySQL Community Server (GPL)
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Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved.
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Oracle is a registered trademark of Oracle Corporation and/or its
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affiliates. Other names may be trademarks of their respective
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owners.
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Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
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mysql>
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mysql> show global variables like '%commit%';
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+-----------------------------------------+-------+
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| Variable_name | Value |
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+-----------------------------------------+-------+
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| autocommit | ON |
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| binlog_group_commit_sync_delay | 0 |
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| binlog_group_commit_sync_no_delay_count | 0 |
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| binlog_order_commits | ON |
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| innodb_api_bk_commit_interval | 5 |
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| innodb_commit_concurrency | 0 |
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| innodb_flush_log_at_trx_commit | 1 |
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| slave_preserve_commit_order | OFF |
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+-----------------------------------------+-------+
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8 rows in set, 1 warning (0.00 sec)
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mysql>
3.修改mysql的配置文件my.ini
我们找到mysql的配置文件my.ini，在里面添加一行记录“autocommit=0”。
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[mysql]
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default-character-set=utf8
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[mysqld]
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max_connections=200
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default-storage-engine=INNODB
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basedir =E:\mysql-5.7.16-winx64\bin
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datadir =E:\mysql-5.7.16-winx64\data
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port = 3306
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autocommit=0
然后重新启动数据库，确认autocommit参数是否为OFF。
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E:\mysql-5.7.16-winx64\bin>net stop mysql
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MySQL 服务正在停止.
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MySQL 服务已成功停止。
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E:\mysql-5.7.16-winx64\bin>net start mysql
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MySQL 服务正在启动 .
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MySQL 服务已经启动成功。
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E:\mysql-5.7.16-winx64\bin>mysql -u root -proot
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mysql: [Warning] Using a password on the command line interface can be insecure.
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Welcome to the MySQL monitor. Commands end with ; or \g.
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Your MySQL connection id is 2
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Server version: 5.7.16 MySQL Community Server (GPL)
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Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved.
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Oracle is a registered trademark of Oracle Corporation and/or its
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affiliates. Other names may be trademarks of their respective
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owners.
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Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
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mysql> show global variables like '%commit%';
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+-----------------------------------------+-------+
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| Variable_name | Value |
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+-----------------------------------------+-------+
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| autocommit | OFF |
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| binlog_group_commit_sync_delay | 0 |
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| binlog_group_commit_sync_no_delay_count | 0 |
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| binlog_order_commits | ON |
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| innodb_api_bk_commit_interval | 5 |
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| innodb_commit_concurrency | 0 |
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| innodb_flush_log_at_trx_commit | 1 |
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| slave_preserve_commit_order | OFF |
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+-----------------------------------------+-------+
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8 rows in set, 1 warning (0.01 sec)
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mysql>
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mysql>
我们看到autocommit参数为OFF，目标达成。
4.数据插入速度提升十倍
以开头提到的那张表为例，4000多条数据，在关闭autocommit参数之前插入时间为101505ms；关闭autocommit参数之后插入时间为8869ms，插入速度提升了十倍还多。
但是这个时间其实还是蛮长的，继续提升！
~~~~~~~ the end~~~~~~~~~
hoegh
2016.11.01
