MYSQL_innodb的加锁机制实验

MYSQL innodb在一定程度上实现了行锁的功能，在功能上与ORACLE差不多。但innodb行锁的实现与oracle不相同，innodb的行锁加在索引上，如果没有索引，整张表都会被锁定，下面是实验过程。
--session 1

mysql> create table test(id int,nick varchar(32)) engine=innodb ;
Query OK, 0 rows affected (0.05 sec)

mysql>
mysql>
mysql> set autocommit=off;
Query OK, 0 rows affected (0.00 sec)

mysql> insert into test values(1,'a');
Query OK, 1 row affected (0.00 sec)

mysql> insert into test values(2,'b'); 
Query OK, 1 row affected (0.00 sec)

mysql> insert into test values(3,'c'); 
Query OK, 1 row affected (0.00 sec)

mysql> insert into test values(4,'d'); 
Query OK, 1 row affected (0.00 sec)

mysql> commit;
Query OK, 0 rows affected (0.00 sec)

mysql> select * from test;
+------+------+
| id   | nick |
+------+------+
|    1 | a    |
|    2 | b    |
|    3 | c    |
|    4 | d    |
+------+------+
4 rows in set (0.00 sec)

mysql>
mysql>
mysql> update test set nick='lock_a' where id=1;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

--session 2
mysql> select * from test;
+------+------+
| id   | nick |
+------+------+
|    1 | a    |
|    2 | b    |
|    3 | c    |
|    4 | d    |
+------+------+
4 rows in set (0.00 sec)

mysql> update test set nick='lock_b' where id=2;
Query OK, 1 row affected (1 min 29.90 sec)   --等待很长的时间，直到session 1提交为止
Rows matched: 1  Changed: 1  Warnings: 0

mysql> commit;
Query OK, 0 rows affected (0.00 sec)

mysql> select * from test;
+------+--------+
| id   | nick   |
+------+--------+
|    1 | lock_a |
|    2 | lock_b |
|    3 | c      |
|    4 | d      |
+------+--------+
4 rows in set (0.00 sec)

如果在test表的id列上创建索引，再观察一下加锁情况
--session 1
mysql> create unique index uk_test_id on test(id);
Query OK, 4 rows affected (0.07 sec)
Records: 4  Duplicates: 0  Warnings: 0

mysql>
mysql> update test set nick='lock_aa' where id=1;                                   
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

更新后，但并不提交，执行session 2的更新语句，发现立刻执行完
--session 2
mysql> update test set nick='lock_bb' where id=2;           
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

--session 1,session 2
mysql> commit;
Query OK, 0 rows affected (0.00 sec)