基于索引上锁，而不是针对选出来的具体的行
root@sakila 10:14:32>show index from tab_no_index \G
*************************** 1. row ***************************
Table: tab_no_index
Non_unique: 1
Key_name: id
Seq_in_index: 1
Column_name: id
Collation: A
Cardinality: 5
Sub_part: NULL
Packed: NULL
Null: YES
Index_type: BTREE
Comment:
Index_comment:
1 row in set (0.00 sec)
第一个会话
root@sakila 10:18:39>select * from tab_no_index where id=1 and name='1' for update;
+------+------+
| id | name |
+------+------+
| 1 | 1 |
+------+------+
1 row in set (0.00 sec)
第二个会话
root@sakila 10:18:42>select * from tab_no_index where id=1 and name='4' for update;
ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction
即使是想更新不同的一条记录，也需要等第一个会话释放锁。
root@sakila 10:14:32>show index from tab_no_index \G
*************************** 1. row ***************************
Table: tab_no_index
Non_unique: 1
Key_name: id
Seq_in_index: 1
Column_name: id
Collation: A
Cardinality: 5
Sub_part: NULL
Packed: NULL
Null: YES
Index_type: BTREE
Comment:
Index_comment:
1 row in set (0.00 sec)
root@sakila 10:18:39>select * from tab_no_index where id=1 and name='1' for update;
+------+------+
| id | name |
+------+------+
| 1 | 1 |
+------+------+
1 row in set (0.00 sec)
第二个会话
root@sakila 10:18:42>select * from tab_no_index where id=1 and name='4' for update;
ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction
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mysql innodb的行锁
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