MYSQL中怎么實現偽行級鎖

本篇文章給大家分享的是有關MYSQL中怎么實現偽行級鎖，小編覺得挺實用的，因此分享給大家學習，希望大家閱讀完這篇文章后可以有所收獲，話不多說，跟著小編一起來看看吧。

 
一.數據準備
mysql> use test;
Database changed
mysql> show create table t_kenyon \G
*************************** 1. row ***************************
       Table: t_kenyon
Create Table: CREATE TABLE `t_kenyon` (
  `id` int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)
 
mysql> set autocommit = 0;
Query OK, 0 rows affected (0.00 sec)
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mysql> show variables like '%autocommit%';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| autocommit    | OFF   |
+---------------+-------+
1 row in set (0.00 sec)
 
mysql> select * from t_kenyon;
+------+
| id   |
+------+
|    1 |
|  123 |
|  789 |
|  345 |
|   78 |
|   78 |
+------+
6 rows in set (0.00 sec)
以上是測試表t_kenyon,設置提交方式為手動提交. 
 
二.過程(開啟兩個session,分別設置autocommit=off) 
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1.session one update
mysql> update t_kenyon set id = 999 where id = 1;
Query OK, 1 row affected (0.04 sec)
Rows matched: 1  Changed: 1  Warnings: 0
 
mysql> select * from t_kenyon;
+------+
| id   |
+------+
|  999 |
|  123 |
|  789 |
|  345 |
|   78 |
|   78 |
+------+
6 rows in set (0.00 sec)
2.session two update
mysql> show variables like 'autocommit';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| autocommit    | OFF   |
+---------------+-------+
1 row in set (0.00 sec)
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mysql> select * from t_kenyon;
+------+
| id   |
+------+
|    1 |
|  123 |
|  789 |
|  345 |
|   78 |
|   78 |
+------+
6 rows in set (0.00 sec)
 
mysql> update t_kenyon set id = 88888 where id = 345;
第二個session更新的值是345，但是也一直被阻塞，直到session1被rollback或者commit,如果session1未做回滾或者提交，session2中的該阻塞在超出mysql的鎖時間限制時自動回滾,該參數為innodb_lock_wait_timeout，默認值50秒 現象如下
ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction
加索引后的測試 
3.session one update
 
mysql> create index ind_kenyon on t_kenyon(id);
Query OK, 0 rows affected (28.58 sec)
Records: 0  Duplicates: 0  Warnings: 0
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mysql> update t_kenyon set id = 999 where id = 1;
Query OK, 1 row affected (0.03 sec)
Rows matched: 1  Changed: 1  Warnings: 0
 
mysql> select * from t_kenyon;
+------+
| id   |
+------+
|   78 |
|   78 |
|  123 |
|  345 |
|  789 |
|  999 |
+------+
6 rows in set (0.00 sec)
4.session two update
 mysql> select * from t_kenyon;
+------+
| id   |
+------+
|    1 |
|   78 |
|   78 |
|  123 |
|  345 |
|  789 |
+------+
6 rows in set (0.00 sec)
  www.2cto.com  
mysql> update t_kenyon set id = 7777 where id = 345;
Query OK, 1 row affected (0.03 sec)
Rows matched: 1  Changed: 1  Warnings: 0
 
mysql> select * from t_kenyon;
+------+
| id   |
+------+
|    1 |
|   78 |
|   78 |
|  123 |
|  789 |
| 7777 |
+------+
6 rows in set (0.00 sec)
執行計劃
mysql> explain select * from t_kenyon where id = 345 \G
*************************** 1. row ***************************
           id: 1  www.2cto.com  
  select_type: SIMPLE
        table: t_kenyon
         type: ref
possible_keys: ind_kenyon
          key: ind_kenyon
      key_len: 5
          ref: const
         rows: 1
        Extra: Using where; Using index
1 row in set (0.00 sec)
可以看到加了索引后，不同的數據更新并沒有被阻塞，實現了真正意義上行鎖 

以上就是MYSQL中怎么實現偽行級鎖，小編相信有部分知識點可能是我們日常工作會見到或用到的。希望你能通過這篇文章學到更多知識。更多詳情敬請關注億速云行業資訊頻道。