表结构：

 CREATE TABLE `test_lock` (
    `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
    PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=60 DEFAULT CHARSET=utf8

隔离级别：REPEATABLE-READ
innodb_locks_unsafe_for_binlog：0

表内容：

 +----+
| id |
+----+
| 12 |
| 39 |
| 59 |
+----+

session1:

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

mysql> select * from test_lock where id <= 39 for update;
+----+
| id |
+----+
| 12 |
| 39 |
+----+
2 rows in set (0.00 sec)

session2:

 mysql> insert into test_lock values(40);

问题：
1. id 是主键，为什么session2还会等待session1的锁呢
2.就算有next-key lock，它不应该是锁住(39, 59]吗，为什么在session2中插入的值是70时还会等待呢。