フルインデックススキャンされる

[Sorarinu]

該当コード：https://github.com/ShuzoN/isucon8-qualify/blob/master/webapp/go/src/torb/app.go#L194

MariaDB [torb]> show index from events;
+--------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table  | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+--------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| events |          0 | PRIMARY  |            1 | id          | A         |          20 |     NULL | NULL   |      | BTREE      |         |               |
+--------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
1 row in set (0.00 sec)

MariaDB [torb]> explain SELECT * FROM events ORDER BY id ASC;
+------+-------------+--------+-------+---------------+---------+---------+------+------+-------+
| id   | select_type | table  | type  | possible_keys | key     | key_len | ref  | rows | Extra |
+------+-------------+--------+-------+---------------+---------+---------+------+------+-------+
|    1 | SIMPLE      | events | index | NULL          | PRIMARY | 4       | NULL |   20 |       |
+------+-------------+--------+-------+---------------+---------+---------+------+------+-------+
1 row in set (0.00 sec)