MySQL行级锁测试
MySQL行级锁测试
MySQL innodb存储引擎使用与Oracle相同的行锁机制，对如何查看系统中存在的行锁情况在下面的实验中，将可以看到。下面是测试过程:
session 1:更新记录
mysql> set autocommit=off;
Query OK, 0 rows affected (0.01 sec)
mysql> update t1 set email='test@test.com' where id=0;
Query OK, 4 rows affected (0.00 sec)
Rows matched: 4 Changed: 4 Warnings: 0
session 2也更新相同的记录,出现等待
mysql> set autocommit=off;
Query OK, 0 rows affected (0.00 sec)
mysql> update t1 set email='abc' where id=0;
session 3:查看系统等待事件:
mysql> show status like '%lock%';
+-------------------------------+---------+
| Variable_name | Value |
+-------------------------------+---------+
| Com_lock_tables | 0 |
| Com_unlock_tables | 0 |
| Innodb_row_lock_current_waits | 1 | --这里
| Innodb_row_lock_time | 0 |
| Innodb_row_lock_time_avg | 0 |
| Innodb_row_lock_time_max | 0 |
| Innodb_row_lock_waits | 1 |
| Key_blocks_not_flushed | 0 |
| Key_blocks_unused | 14497 |
| Key_blocks_used | 0 |
| Qcache_free_blocks | 1 |
| Qcache_total_blocks | 1 |
| Table_locks_immediate | 2070991 |
| Table_locks_waited | 2 |
+-------------------------------+---------+
14 rows in set (0.01 sec)
session 1:提交记录
mysql> commit;
Query OK, 0 rows affected (0.01 sec)
session 2:update立刻完成
mysql> update t1 set email='abc' where id=0;
Query OK, 4 rows affected (2 min 43.44 sec)--这么长时间完成更新操作
Rows matched: 4 Changed: 4 Warnings: 0
session 3:再次查看系统等待事件
mysql> show status like '%lock%';
+-------------------------------+---------+
| Variable_name | Value |
+-------------------------------+---------+
| Com_lock_tables | 0 |
| Com_unlock_tables | 0 |
| Innodb_row_lock_current_waits | 0 | --这里为0
| Innodb_row_lock_time | 163436 |
| Innodb_row_lock_time_avg | 163436 |
| Innodb_row_lock_time_max | 163436 |
| Innodb_row_lock_waits | 1 |
| Key_blocks_not_flushed | 0 |
| Key_blocks_unused | 14497 |
| Key_blocks_used | 0 |
| Qcache_free_blocks | 1 |
| Qcache_total_blocks | 1 |
| Table_locks_immediate | 2070991 |
| Table_locks_waited | 2 |
+-------------------------------+---------+
|
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