一、外鍵鎖
一般在插入大量數據的時候要先禁用外鍵（SET foreign_key_checks = 0）。那是爲什麼呢？下面我們對此進行研究：
表結構：
CREATE TABLE `foreign_no1` ( `id` int(11) NOT NULL DEFAULT '0', `no` int(11) DEFAULT NULL, PRIMARY KEY (`id`))
CREATE TABLE `foreign_no2` ( `id` int(11) NOT NULL DEFAULT '0', `no` int(11) DEFAULT NULL, PRIMARY KEY (`id`), CONSTRAINT `foreign_no2_ibfk_2` FOREIGN KEY (`id`) REFERENCES`foreign_no1` (`id`) ON DELETE CASCADE)
數據：
mysql> select * from foreign_no1; +----+------+ | id | no | +----+------+ | 1| 2 | | 2| 3 | +----+------+
mysql> select * from foreign_no2; +----+------+ | id | no | +----+------+ | 1| 5 | +----+------+
Delete 操作
| 子表 | 父表 |
mysql> start transaction; Query OK, 0 rows affected (0.00 sec)
mysql> delete from foreign_no2 whereid=1; Query OK, 1 row affected (0.00 sec) | mysql> start transaction; Query OK, 0 rows affected (0.00 sec)
mysql> select * from foreign_no1 whereid=1 lock in share mode; ##父表可以查詢 +----+------+ | id | no | +----+------+ | 1| 2 | +----+------+ 1 row in set (0.00 sec)
mysql> start transaction; Query OK, 0 rows affected (0.00 sec)
mysql> delete from foreign_no1 whereid=1; ##父表不允許做更改操作 ^CCtrl-C -- sending "KILL QUERY78" to server ... Ctrl-C -- query aborted. ERROR 1317 (70100): Query execution wasinterrupted mysql> rollback |
可以看到子表做delete操作，父表可以做select 但不能運行dml語句，因爲子表對父表相關的一行記錄做了讀鎖操作，只允許讀，不能修改，以此來保障父表和子表的數據完整性。
| 父表 |
mysql> start transaction; Query OK, 0 rows affected (0.00 sec)
mysql> delete from foreign_no1 whereid=2; Query OK, 1 row affected (0.00 sec) |
可以看到父表鎖對應的一行做了讀鎖操作，其餘記錄行依然能更新。
Insert操作
| 子表 | 父表 |
mysql> start transaction; Query OK, 0 rows affected (0.00 sec)
mysql> insert into foreign_no2 values (3,5); Query OK, 1 row affected (0.00 sec) | mysql> start transaction; Query OK, 0 rows affected (0.00 sec)
mysql> delete from foreign_no1 where id=3; ^CCtrl-C -- sending "KILL QUERY78" to server ... Ctrl-C -- query aborted. ERROR 1317 (70100): Query execution wasinterrupted mysql> update foreign_no1 set id=8 where id=3; ^CCtrl-C -- sending "KILL QUERY78" to server ... Ctrl-C -- query aborted. ERROR 1317 (70100): Query execution wasinterrupted |
可以發現insert 也和delete情況一樣，父表鎖對應的一行做了讀鎖操作。
Update操作
| 子表 | 父表 |
mysql> start transaction; mysql> update foreign_no2 set id =3where id=2; Query OK, 1 row affected (0.02 sec) Rows matched: 1 Changed: 1 Warnings: 0 | mysql> delete from foreign_no1 whereid=3; ^CCtrl-C -- sending "KILL QUERY78" to server ... Ctrl-C -- query aborted. ERROR 1317 (70100): Query execution wasinterrupted mysql> delete from foreign_no1 whereid=2; ERROR 1205 (HY000): Lock wait timeoutexceeded; try restarting transaction |
可以看到被update相關的父表兩條記錄都加了鎖。
在對子表進行操作時，外鍵鎖將會在父表中鎖住相應的記錄來保證數據完整性。所以爲了防止在子表更新時對父表數據鎖的現象發生，一般在大量插入數據時會禁用外鍵約束。
二、自增鎖
insert一般分爲兩種，
第一種：簡單的insert。插入之前知道插入的行數。如：insert ,replace
第二種：塊的insert。插入之前不知道多少插入的行數。如:insert select ，load data
簡單insert不會生成auto-inc locking（自增鎖）。那塊的insert 會不會呢？
mysql> show create tableFreedom.key_id_inre; +-------------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | Table | Create Table | +-------------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | key_id_inre | CREATE TABLE `key_id_inre`( `id` int(11) NOT NULL AUTO_INCREMENT, `no` int(11) DEFAULT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=1638392DEFAULT CHARSET=utf8 | +-------------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| 事務一 | 事務二 |
mysql> insert into Freedom.key_id (id)select id from sanguo_te.players;
| mysql> insert into key_id_inre (no)values (100); ^CCtrl-C -- sending "KILL QUERY78" to server ... Ctrl-C -- query aborted. ERROR 1317 (70100): Query execution wasinterrupted mysql> delete from foreign_no1 whereid=2; ERROR 1205 (HY000): Lock wait timeoutexceeded; try restarting transaction |
auto-inc locking不會等到事務提交後才釋放，而是插入好以後立即釋放。當事務一，開始insert 時，事務二被鎖住，當事務一insert 結束時，事務二insert被解鎖並插入成功。這樣的目的是Mysql通過auto-inc locking來保障塊插入是連續的所以在此期間不能有新記錄插入。如果列中沒有自增量，auto-inc locking鎖自然也不會存在。