本篇内容介绍了“mysql互为主从的环境为什么会出现数据不一致”的有关知识，在实际案例的操作过程中，不少人都会遇到这样的困境，接下来就让小编带领大家学习一下如何处理这些情况吧！希望大家仔细阅读，能够学有所成！
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。
由 dawei
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