mysql互為主從的環境，更新一條語句同時提交，為什麽會出現數據不一致？
mysql互為主從的環境，更新一條語句同時提交，為什麽會出現數據不一致？
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同時提交，復制不會報錯，但是m1和m2的數據不一致，為什麽？
因為sql_thread線程根據主鍵更新數據，不會校驗行數據
如何避免這種問題：
只在單節點進行寫入，如 keepalived+雙主，MGR，PXC如果多節點寫入都有這種問題發生。
例1：
表有主鍵和自增的情況：
[email protected] [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: |
[email protected] [testdb]>select * from t1; +----+------+ | c1 | c2 | +----+------+ | 1 | aaa | | 2 | bbb | | 3 | ccc | | 4 | ccc | | 6 | ddd | | 8 | eee | +----+------+ | [email protected] [testdb]>select * from t1; +----+------+ | c1 | c2 | +----+------+ | 1 | aaa | | 2 | bbb | | 3 | ccc | | 4 | ccc | | 6 | ddd | | 8 | eee | +----+------+ |
| [email protected] [testdb]>begin; | [email protected] [testdb]>begin; |
| [email protected] [testdb]>update t1 set c2=‘b1‘ where c1=2; | [email protected] [testdb]>update t1 set c2=‘b2‘ where c1=2; |
[email protected] [testdb]>select * from t1; +----+------+ | c1 | c2 | +----+------+ | 1 | aaa | | 2 | b1 | | 3 | ccc | | 4 | ccc | | 6 | ddd | | 8 | eee | +----+------+ | [email protected] [testdb]>select * from t1; +----+------+ | c1 | c2 | +----+------+ | 1 | aaa | | 2 | b2 | | 3 | ccc | | 4 | ccc | | 6 | ddd | | 8 | eee | +----+------+ |
| [email protected] [testdb]>commit; | [email protected] [testdb]>commit; |
[email protected] [testdb]>select * from t1; +----+------+ | c1 | c2 | +----+------+ | 1 | aaa | | 2 | b2 | | 3 | ccc | | 4 | ccc | | 6 | ddd | | 8 | eee | +----+------+ | [email protected] [testdb]>select * from t1; +----+------+ | c1 | c2 | +----+------+ | 1 | aaa | | 2 | b1 | | 3 | ccc | | 4 | ccc | | 6 | ddd | | 8 | eee | +----+------+ |
總結：update一條記錄同時提交，有主鍵的情況下，sql_thread是根據主鍵匹配行記錄，不會校驗行數據，所以m1更新了m2中表的記錄，m2更新了m1中表的記錄。
例2：有沒有主鍵同時更新一行數據的情況：
[email protected] [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 |
[email protected] [testdb]>select * from t2; +------+------+ | c1 | c2 | +------+------+ | 1 | aaa | | 2 | bbb | +------+------+ | [email protected] [testdb]>select * from t2; +------+------+ | c1 | c2 | +------+------+ | 1 | aaa | | 2 | bbb | +------+------+ |
| [email protected] [testdb]>begin; | [email protected] [testdb]>begin; |
| [email protected] [testdb]>update t2 set c2=‘b1‘ where c1=2; | [email protected] [testdb]>update t2 set c2=‘b2‘ where c1=2; |
[email protected] [testdb]>select * from t2; +------+------+ | c1 | c2 | +------+------+ | 1 | aaa | | 2 | b1 | +------+------+ | [email protected] [testdb]>select * from t2; +------+------+ | c1 | c2 | +------+------+ | 1 | aaa | | 2 | b2 | +------+------+ |
| [email protected] [testdb]>commit; | [email protected] [testdb]>commit; |
[email protected] [testdb]>select * from t2; +------+------+ | c1 | c2 | +------+------+ | 1 | aaa | | 2 | b1 | +------+------+ | [email protected] [testdb]>select * from t2; +------+------+ | c1 | c2 | +------+------+ | 1 | aaa | | 2 | b2 | +------+------+ |
[email protected] [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 | [email protected] [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 |
總結：update一條記錄同時提交，有沒有主鍵的情況下，sql_thread是根據全表掃描匹配行記錄，所以m1更新在m2中找不到需要更新的行，報1032錯誤，m2更新在m1中找不到需要更新的行，也報1032錯誤。
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mysql互為主從的環境，更新一條語句同時提交，為什麽會出現數據不一致？