我有一个MySQL数据库，结构如下：

mysql> describe company;
+-------+-------------+------+-----+---------+----------------+
| Field | Type        | Null | Key | Default | Extra          |
+-------+-------------+------+-----+---------+----------------+
| id    | int         | NO   | PRI | NULL    | auto_increment |
| name  | varchar(50) | NO   |     | NULL    |                |
+-------+-------------+------+-----+---------+----------------+

mysql> describe nameserver;
+-----------+--------------+------+-----+---------+----------------+
| Field     | Type         | Null | Key | Default | Extra          |
+-----------+--------------+------+-----+---------+----------------+
| id        | int          | NO   | PRI | NULL    | auto_increment |
| companyId | int          | NO   | MUL | NULL    |                |
| ns        | varchar(250) | NO   | MUL | NULL    |                |
+-----------+--------------+------+-----+---------+----------------+

mysql> describe domain;
+--------------+--------------+------+-----+-------------------+-------------------+
| Field        | Type         | Null | Key | Default           | Extra             |
+--------------+--------------+------+-----+-------------------+-------------------+
| id           | int          | NO   | PRI | NULL              | auto_increment    |
| nameserverId | int          | NO   | MUL | NULL              |                   |
| domain       | varchar(250) | NO   | MUL | NULL              |                   |
| tld          | varchar(20)  | NO   | MUL | NULL              |                   |
| createDate   | datetime     | NO   |     | CURRENT_TIMESTAMP | DEFAULT_GENERATED |
| updatedAt    | datetime     | YES  |     | NULL              |                   |
| status       | tinyint      | NO   |     | NULL              |                   |
| fileNo       | smallint     | NO   | MUL | NULL              |                   |
+--------------+--------------+------+-----+-------------------+-------------------+

索引结构：

-- Indexes for table `company`
--
ALTER TABLE `company`
  ADD PRIMARY KEY (`id`);

--
-- Indexes for table `domain`
--
ALTER TABLE `domain`
  ADD PRIMARY KEY (`id`),
  ADD KEY `nameserver` (`nameserverId`),
  ADD KEY `domain` (`domain`),
  ADD KEY `tld` (`tld`),
  ADD KEY `fileNo` (`fileNo`);

--
-- Indexes for table `nameserver`
--
ALTER TABLE `nameserver`
  ADD PRIMARY KEY (`id`),
  ADD KEY `company` (`companyId`),
  ADD KEY `ns` (`ns`);

--
-- AUTO_INCREMENT for dumped tables
--

--
-- AUTO_INCREMENT for table `company`
--
ALTER TABLE `company`
  MODIFY `id` int NOT NULL AUTO_INCREMENT;

--
-- AUTO_INCREMENT for table `domain`
--
ALTER TABLE `domain`
  MODIFY `id` int NOT NULL AUTO_INCREMENT;

--
-- AUTO_INCREMENT for table `nameserver`
--
ALTER TABLE `nameserver`
  MODIFY `id` int NOT NULL AUTO_INCREMENT;

--
-- Constraints for dumped tables
--

--
-- Constraints for table `domain`
--
ALTER TABLE `domain`
  ADD CONSTRAINT `nameserver` FOREIGN KEY (`nameserverId`) REFERENCES `nameserver` (`id`);

--
-- Constraints for table `nameserver`
--
ALTER TABLE `nameserver`
  ADD CONSTRAINT `company` FOREIGN KEY (`companyId`) REFERENCES `company` (`id`);

数据量如下：

domain table about 500 millions records
nameserver table about 2 millions records

运行此查询大约需要4个小时才能得到结果：

SELECT distinct domain FROM domain 
INNER join nameserver on nameserver.id = domain.nameserverId
 WHERE nameserver.companyId = 2

上述查询的解释结果：

+----+-------------+------------+------------+------+-------------------

+------------+---------+-----------------------+------+----------+------------------------------+
| id | select_type | table      | partitions | type | possible_keys     | key        | key_len | ref                   | rows | filtered | Extra                        |
+----+-------------+------------+------------+------+-------------------+------------+---------+-----------------------+------+----------+------------------------------+
|  1 | SIMPLE      | nameserver | NULL       | ref  | PRIMARY,company   | company    | 4       | const                 | 1738 |   100.00 | Using index; Using temporary |
|  1 | SIMPLE      | domain     | NULL       | ref  | nameserver,domain | nameserver | 4       | tldzone.nameserver.id |  716 |   100.00 | NULL                         |
+----+-------------+------------+------------+------+-------------------+------------+---------+-----------------------+------+----------+------------------------------+

我的问题是如何提高从这个数据库获取查询的速度？
对我来说，改变DB结构甚至用另一个DBMS替换它是可能的。
MySQL运行在一个8.0 GB RAM和双核CPU的VPS上。