MySQL中InnoDB的间隙锁问题

mysql> SHOW CREATE TABLE preferences \G
*************************** 1. row ***************************
    Table: preferences
Create Table: CREATE TABLE `preferences` (
 `numericId` int(10) unsigned NOT NULL,
 `receiveNotifications` tinyint(1) DEFAULT NULL,
 PRIMARY KEY (`numericId`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.00 sec)
mysql> BEGIN;
Query OK, 0 rows affected (0.00 sec)
mysql> SELECT COUNT(*) FROM preferences;
+----------+
| COUNT(*) |
+----------+
|    0 |
+----------+
1 row in set (0.01 sec)
mysql> UPDATE preferences SET receiveNotifications='1' WHERE numericId = '2';
Query OK, 0 rows affected (0.01 sec)
Rows matched: 0 Changed: 0 Warnings: 0

InnoDB状态显示这个UPDATE在主索引记录上持有了一个X锁：
 

---TRANSACTION 4A18101, ACTIVE 12 sec
2 lock struct(s), heap size 376, 1 row lock(s)
MySQL thread id 3, OS thread handle 0x7ff2200cd700, query id 35 localhost msandbox
Trx read view will not see trx with id >= 4A18102, sees < 4A18102
TABLE LOCK table `test`.`preferences` trx id 4A18101 lock mode IX
RECORD LOCKS space id 31766 page no 3 n bits 72 index `PRIMARY` of table `test`.`preferences` trx id 4A18101 lock_mode X

mysql1> BEGIN;
Query OK, 0 rows affected (0.00 sec)
mysql1> UPDATE preferences SET receiveNotifications='1' WHERE numericId = '1';
Query OK, 0 rows affected (0.00 sec)
Rows matched: 0 Changed: 0 Warnings: 0
mysql2> BEGIN;
Query OK, 0 rows affected (0.00 sec)
mysql2> UPDATE preferences SET receiveNotifications='1' WHERE numericId = '2';
Query OK, 0 rows affected (0.00 sec)
Rows matched: 0 Changed: 0 Warnings: 0
mysql1> INSERT INTO preferences (numericId, receiveNotifications) VALUES ('1', '1'); -- This one goes into LOCK WAIT
mysql2> INSERT INTO preferences (numericId, receiveNotifications) VALUES ('2', '1');
ERROR 1213 (40001): Deadlock found when trying to get lock; try restarting transaction