某数据表只有两条记录，怎么占用空间有1.5MB?

是不是phpMyAdmin有bug，显示的数据表大小不对呢？以下是细节：表结构：
desc dis_sessions
    -> ;
+--------------+-----------------------+------+-----+---------+-------+
| Field        | Type                  | Null | Key | Default | Extra |
+--------------+-----------------------+------+-----+---------+-------+
| sid          | char(6)               | NO   | PRI |         |       |
| ip1          | tinyint(3) unsigned   | NO   |     | 0       |       |
| ip2          | tinyint(3) unsigned   | NO   |     | 0       |       |
| ip3          | tinyint(3) unsigned   | NO   |     | 0       |       |
| ip4          | tinyint(3) unsigned   | NO   |     | 0       |       |
| uid          | mediumint(8) unsigned | NO   | MUL | 0       |       |
| username     | char(15)              | NO   |     |         |       |
| groupid      | smallint(6) unsigned  | NO   |     | 0       |       |
| styleid      | smallint(6) unsigned  | NO   |     | 0       |       |
| invisible    | tinyint(1)            | NO   |     | 0       |       |
| action       | tinyint(1) unsigned   | NO   |     | 0       |       |
| lastactivity | int(10) unsigned      | NO   |     | 0       |       |
| lastolupdate | int(10) unsigned      | NO   |     | 0       |       |
| pageviews    | smallint(6) unsigned  | NO   |     | 0       |       |
| seccode      | mediumint(6) unsigned | NO   |     | 0       |       |
| fid          | smallint(6) unsigned  | NO   |     | 0       |       |
| tid          | mediumint(8) unsigned | NO   |     | 0       |       |
| bloguid      | mediumint(8) unsigned | NO   | MUL | 0       |       |
+--------------+-----------------------+------+-----+---------+-------+
18 rows in set (0.31 sec)好像都没用到大的结构么phpmyadmin中显示
dis_sessions  浏览   结构  搜索   插入  清空   删除 2 MEMORY utf8_general_ci 1.5 MB 98 字节这是怎么了？
两条记录不至于占用  1.5MB空间吧？