mysql 提交讀 可重複讀
阿新 • • 發佈:2019-02-08
環境
mysql> select version();
+------------+
| version() |
+------------+
| 5.6.31-log |
+------------+
1 row in set (0.00 sec)
提交讀
檢視當前資料庫隔離級別
mysql> select @@global.tx_isolation,@@tx_isolation;
+-----------------------+----------------+
| @@global.tx_isolation | @@tx_isolation |
+-----------------------+----------------+
| READ-COMMITTED | READ-COMMITTED |
+-----------------------+----------------+
1 row in set (0.00 sec)
檢視測試表結構
mysql> show create table t\G;
*************************** 1. row ***************************
Table: t
Create Table: CREATE TABLE `t` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`comment` varchar(30) DEFAULT NULL,
`time` datetime DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)
解決髒讀問題,但是會出現不可重複讀
#session 1 session 2
mysql> begin; mysql> begin;
Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec)
mysql> select * from t;
Empty set (0.00 sec)
mysql> insert into t(comment,time) values ('r1',now());
Query OK, 1 row affected (0.00 sec)
mysql> commit;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from t;
+----+---------+---------------------+
| id | comment | time |
+----+---------+---------------------+
| 1 | r1 | 2016-09-23 15:56:17 |
+----+---------+---------------------+
1 row in set (0.00 sec)
mysql> commit;
Query OK, 0 rows affected (0.00 sec)
可重複讀
設定全域性的隔離級別為REPEATABLE-READ
mysql> set global tx_isolation='REPEATABLE-READ';
Query OK, 0 rows affected (0.00 sec)
清空測試資料
mysql> truncate table t;
Query OK, 0 rows affected (0.03 sec)
重複執行上面的實驗,可見在可重複讀的隔離級別下,不可重複讀得到了解決
#session 1 session 2
mysql> begin; mysql> begin;
Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec)
mysql> select * from t;
Empty set (0.00 sec)
mysql> insert into t(comment,time) values ('r2',now());
Query OK, 1 row affected (0.00 sec)
mysql> commit;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from t;
Empty set (0.00 sec)
mysql> commit;
Query OK, 0 rows affected (0.00 sec)
清空測試資料
mysql> truncate table t;
Query OK, 0 rows affected (0.03 sec)
進一步測試,幻讀現象出現
#session 1 session 2
mysql> begin; mysql> begin;
Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec)
mysql> select * from t;
Empty set (0.00 sec)
mysql> insert into t(comment,time) values ('r3',now());
Query OK, 1 row affected (0.00 sec)
mysql> commit;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from t;
Empty set (0.00 sec)
mysql> update t set comment='c3';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select * from t;
+----+---------+---------------------+
| id | comment | time |
+----+---------+---------------------+
| 1 | c3 | 2016-09-23 16:53:28 |
+----+---------+---------------------+
1 row in set (0.00 sec)
mysql> commit;
Query OK, 0 rows affected (0.00 sec)