mysql互为主从的环境，更新一条语句同时提交，为什么会出现数据不一致（） mysql互为主从的环境，更新一条

mysql互为主从的环境，更新一条语句同时提交，为什么会出现数据不一致？

m1：

begin;
update t1 set c2='b1' where c1=2;
commit;

m2:

begin;
update t1 set c2='b2' where c1=2;
commit;

m1和m2同时提交，复制不会报错，但是m1和m2的数据不一致，为什么？
因为sql_thread线程根据主键更新数据，不会校验行数据

如何避免这种问题：
只在单节点进行写入，如 keepalived+双主，MGR，PXC如果多节点写入都有这种问题发生。

例1：
表有主键和自增的情况：
root@localhost [testdb]>show create table t1\G
*************************** 1. row ***************************
Table: t1
Create Table: CREATE TABLE `t1` (
`c1` int(11) NOT NULL AUTO_INCREMENT,
`c2` varchar(10) DEFAULT NULL,
PRIMARY KEY (`c1`)
) ENGINE=InnoDB AUTO_INCREMENT=9 DEFAULT CHARSET=utf8

m1:	m2:
root@localhost [testdb]>select * from t1; +----+------+ \| c1 \| c2\| +----+------+ \|1 \| aaa\| \|2 \| bbb\| \|3 \| ccc\| \|4 \| ccc\| \|6 \| ddd\| \|8 \| eee\| +----+------+	root@localhost [testdb]>select * from t1; +----+------+ \| c1 \| c2\| +----+------+ \|1 \| aaa\| \|2 \| bbb\| \|3 \| ccc\| \|4 \| ccc\| \|6 \| ddd\| \|8 \| eee\| +----+------+
root@localhost [testdb]>begin;	root@localhost [testdb]>begin;
root@localhost [testdb]>update t1 set c2='b1' where c1=2;	root@localhost [testdb]>update t1 set c2='b2' where c1=2;
root@localhost [testdb]>select * from t1; +----+------+ \| c1 \| c2\| +----+------+ \|1 \| aaa\| \|2 \| b1\| \|3 \| ccc\| \|4 \| ccc\| \|6 \| ddd\| \|8 \| eee\| +----+------+	root@localhost [testdb]>select * from t1; +----+------+ \| c1 \| c2\| +----+------+ \|1 \| aaa\| \|2 \| b2\| \|3 \| ccc\| \|4 \| ccc\| \|6 \| ddd\| \|8 \| eee\| +----+------+
root@localhost [testdb]>commit;	root@localhost [testdb]>commit;
root@localhost [testdb]>select * from t1; +----+------+ \| c1 \| c2\| +----+------+ \|1 \| aaa\| \|2 \| b2\| \|3 \| ccc\| \|4 \| ccc\| \|6 \| ddd\| \|8 \| eee\| +----+------+	root@localhost [testdb]>select * from t1; +----+------+ \| c1 \| c2\| +----+------+ \|1 \| aaa\| \|2 \| b1\| \|3 \| ccc\| \|4 \| ccc\| \|6 \| ddd\| \|8 \| eee\| +----+------+

总结：update一条记录同时提交，有主键的情况下，sql_thread是根据主键匹配行记录，不会校验行数据，所以m1更新了m2中表的记录，m2更新了m1中表的记录。

例2：有没有主键同时更新一行数据的情况：

root@localhost [testdb]>show create table t2\G
*************************** 1. row ***************************
Table: t2
Create Table: CREATE TABLE `t2` (
`c1` int(11) DEFAULT NULL,
`c2` varchar(20) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8

m1	m2
root@localhost [testdb]>select * from t2; +------+------+ \| c1\| c2\| +------+------+ \|1 \| aaa\| \|2 \| bbb\| +------+------+	root@localhost [testdb]>select * from t2; +------+------+ \| c1\| c2\| +------+------+ \|1 \| aaa\| \|2 \| bbb\| +------+------+
root@localhost [testdb]>begin;	root@localhost [testdb]>begin;
root@localhost [testdb]>update t2 set c2='b1' where c1=2;	root@localhost [testdb]>update t2 set c2='b2' where c1=2;
root@localhost [testdb]>select * from t2; +------+------+ \| c1\| c2\| +------+------+ \|1 \| aaa\| \|2 \| b1\| +------+------+	root@localhost [testdb]>select * from t2; +------+------+ \| c1\| c2\| +------+------+ \|1 \| aaa\| \|2 \| b2\| +------+------+
root@localhost [testdb]>commit;	root@localhost [testdb]>commit;
root@localhost [testdb]>select * from t2; +------+------+ \| c1\| c2\| +------+------+ \|1 \| aaa\| \|2 \| b1\| +------+------+	root@localhost [testdb]>select * from t2; +------+------+ \| c1\| c2\| +------+------+ \|1 \| aaa\| \|2 \| b2\| +------+------+
root@localhost [testdb]>show slave status\G Last_Errno: 1032 Last_Error: Could not execute Update_rows event on table testdb.t2; Can't find record in 't2', Error_code: 1032; handler error HA_ERR_END_OF_FILE; the event's master log mysql-bin.000013, end_log_pos 759	root@localhost [testdb]>show slave status\G Last_Errno: 1032 Last_Error: Could not execute Update_rows event on table testdb.t2; Can't find record in 't2', Error_code: 1032; handler error HA_ERR_END_OF_FILE; the event's master log mysql-bin.000026, end_log_pos 3064

总结：update一条记录同时提交，有没有主键的情况下，sql_thread是根据全表扫描匹配行记录，所以m1更新在m2中找不到需要更新的行，报1032错误，m2更新在m1中找不到需要更新的行，也报1032错误。

【mysql互为主从的环境，更新一条语句同时提交，为什么会出现数据不一致（）】转载于:https://blog.51cto.com/darrenmemos/1924073