这是为了多 tidb server 写入不冲突用的，本例应该不涉及，而且自增步长也是1.
tidb> show variables like 'auto_%';
+--------------------------+-------+
| Variable_name | Value |
+--------------------------+-------+
| auto_increment_increment | 1 |
| auto_increment_offset | 1 |
| autocommit | ON |
| automatic_sp_privileges | 1 |
+--------------------------+-------+
4 rows in set (0.00 sec)