mysqldump主要参数分析

mysqldump是逻辑备份，较适合备份数据量小的库。今天我们来看看几个比较常用的重要参数，并分析它们都做了什么，需要打开general_log。

set global general_log = 1;
+------------------+--------------------------------------+
| Variable_name    | Value                                |
+------------------+--------------------------------------+
| general_log      | ON                                   |
| general_log_file | /data/mysql/mysql3317/data/bogon.log |
+------------------+--------------------------------------+

表结构如下：

*************************** 1. row ***************************
       Table: zhangshuo
Create Table: CREATE TABLE `zhangshuo` (
  `id` int(11) DEFAULT NULL,
  `name` varchar(50) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

1.不加参数备份zhangshuo表：

[root@bogon ~]# /usr/local/mysql/bin/mysqldump -S /tmp/mysql3317.sock zhangshuo zhangshuo >/tmp/test.sql　

                    4 Init DB   zhangshuo
                    4 Query     SHOW TABLES LIKE 'zhangshuo'
                    4 Query     LOCK TABLES `zhangshuo` READ /*!32311 LOCAL */
                    4 Query     show table status like 'zhangshuo'
                    4 Query     SET SQL_QUOTE_SHOW_CREATE=1
                    4 Query     SET SESSION character_set_results = 'binary'
                    4 Query     show create table `zhangshuo`
                    4 Query     SET SESSION character_set_results = 'utf8'
                    4 Query     show fields from `zhangshuo`
                    4 Query     SELECT /*!40001 SQL_NO_CACHE */ * FROM `zhangshuo`
                    4 Query     SET SESSION character_set_results = 'binary'
                    4 Query     use `zhangshuo`
                    4 Query     select @@collation_database
                    4 Query     SHOW TRIGGERS LIKE 'zhangshuo'
                    4 Query     SET SESSION character_set_results = 'utf8'
                    4 Query     UNLOCK TABLES
                    4 Quit

2.使用--single-transaction参数：

                    5 Query     /*!40100 SET @@SQL_MODE='' */
                    5 Query     /*!40103 SET TIME_ZONE='+00:00' */
                    5 Query     SET SESSION TRANSACTION ISOLATION LEVEL REPEATABLE READ
                    5 Query     START TRANSACTION /*!40100 WITH CONSISTENT SNAPSHOT */
                    5 Query     SHOW VARIABLES LIKE 'ndbinfo\_version'
                    5 Init DB   zhangshuo
                    5 Query     SHOW TABLES LIKE 'zhangshuo'
                    5 Query     SAVEPOINT sp
                    5 Query     show table status like 'zhangshuo'
                    5 Query     SET SQL_QUOTE_SHOW_CREATE=1
                    5 Query     SET SESSION character_set_results = 'binary'
                    5 Query     show create table `zhangshuo`
                    5 Query     SET SESSION character_set_results = 'utf8'
                    5 Query     show fields from `zhangshuo`
                    5 Query     SELECT /*!40001 SQL_NO_CACHE */ * FROM `zhangshuo`
                    5 Query     SET SESSION character_set_results = 'binary'
                    5 Query     use `zhangshuo`
                    5 Query     select @@collation_database
                    5 Query     SHOW TRIGGERS LIKE 'zhangshuo'
                    5 Query     SET SESSION character_set_results = 'utf8'
                    5 Query     ROLLBACK TO SAVEPOINT sp
                    5 Query     RELEASE SAVEPOINT sp
                    5 Quit

我们看到事物隔离级别改为RR，使用innodb的事物隔离性防止发生幻读。

3.使用--master-data=2 --single-transaction参数：

[root@bogon ~]# /usr/local/mysql/bin/mysqldump --single-transaction --master-data=2 -S /tmp/mysql3317.sock zhangshuo zhangshuo >/tmp/test2.sql　

6 Connect   root@localhost on
                    6 Query     /*!40100 SET @@SQL_MODE='' */
                    6 Query     /*!40103 SET TIME_ZONE='+00:00' */
                    6 Query     FLUSH /*!40101 LOCAL */ TABLES
                    6 Query     FLUSH TABLES WITH READ LOCK
                    6 Query     SET SESSION TRANSACTION ISOLATION LEVEL REPEATABLE READ
                    6 Query     START TRANSACTION /*!40100 WITH CONSISTENT SNAPSHOT */
                    6 Query     SHOW VARIABLES LIKE 'gtid\_mode'
                    6 Query     SHOW MASTER STATUS
                    6 Query     UNLOCK TABLES
                    6 Query     SHOW VARIABLES LIKE 'ndbinfo\_version'
                    6 Init DB   zhangshuo
                    6 Query     SHOW TABLES LIKE 'zhangshuo'
                    6 Query     SAVEPOINT sp
                    6 Query     show table status like 'zhangshuo'
                    6 Query     SET SQL_QUOTE_SHOW_CREATE=1
                    6 Query     SET SESSION character_set_results = 'binary'
                    6 Query     show create table `zhangshuo`
                    6 Query     SET SESSION character_set_results = 'utf8'
                    6 Query     show fields from `zhangshuo`
                    6 Query     SELECT /*!40001 SQL_NO_CACHE */ * FROM `zhangshuo`
                    6 Query     SET SESSION character_set_results = 'binary'
                    6 Query     use `zhangshuo`
                    6 Query     select @@collation_database
                    6 Query     SHOW TRIGGERS LIKE 'zhangshuo'
                    6 Query     SET SESSION character_set_results = 'utf8'
                    6 Query     ROLLBACK TO SAVEPOINT sp
                    6 Query     RELEASE SAVEPOINT sp

首先下发flush table with read lock（关闭已经打开的表）全局读锁后将事物隔离级别改为RR，并执行START TRANSACTION /*!40100 WITH CONSISTENT SNAPSHOT */创建一次性快照，接着查看是否开启GTID，获取gtid执行位置。数据备份时定义断点 SAVEPOINT sp，做完重新回到这个位置并开始下一张表，最后释放掉断点。

使用--master-data=2后我们再看看备份的SQL，可看到binlog执行位置，很方便搭建主从。

[root@bogon tmp]# grep "CHANGE MASTER TO" /tmp/test2.sql 
-- CHANGE MASTER TO MASTER_LOG_FILE='mysql-bin.000006', MASTER_LOG_POS=667;

总结：

备份innodb表推荐参数如下：

[root@bogon tmp]# /usr/local/mysql/bin/mysqldump --single-transaction --master-data=2 -S /tmp/mysql3317.sock zhangshuo zhangshuo >/tmp/test2.sql