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。
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