优化MySql查询:订购时太慢

Question

(编辑)有关应用程序的更多详细信息,请参阅: 简单但繁重的应用程序消耗大量资源.如何优化？ (采用的解决方案是使用连接和全文搜索)

我有以下查询在25秒内运行大约500.000行.如果我删除了ORDER,则需要0.5秒.

Fisrt测试

保持ORDER和删除所有t.和tu.列,查询需要7秒.

第二次测试

如果我在i.created_at字段中添加或删除INDEX,则响应时间保持不变.

查询:

**已编辑:我已注意到按顺序排列并按顺序排列查询(我在查询中也获得了一点点改变连接.增益为10秒,但问题仍然存在).通过修改,EXPLAIN已经停止返回filesort,但仍然返回"使用临时"**

SELECT SQL_NO_CACHE
        DISTINCT `i`.`id`, 
        `i`.`entity`, 
        `i`.`created_at`, 
        `i`.`collected_at`, 

        `t`.`status_id` AS  `twt_status_id`, 
        `t`.`user_id` AS `twt_user_id`, 
        `t`.`content` AS `twt_content`, 
        `tu`.`id` AS `twtu_id`, 
        `tu`.`screen_name` AS `twtu_screen_name`, 
        `tu`.`profile_image` AS `twtu_profile_image`


        FROM `mtrt_items` AS `i`

        LEFT JOIN `mtrt_users` AS `u` ON i.user_id =u.id

        LEFT JOIN `twt_tweets_content` AS `t` ON t.id =i.id
        LEFT JOIN `twt_users` AS `tu` ON u.id = tu.id

        INNER JOIN `mtrt_items_searches` AS `r` ON i.id =r.item_id
        INNER JOIN `mtrt_searches` AS `s` ON s.id =r.search_id
        INNER JOIN `mtrt_searches_groups` AS `sg` ON sg.search_id =s.id
        INNER JOIN `mtrt_search_groups` AS `g` ON sg.group_id =g.id
        INNER JOIN `account_clients` AS `c` ON g.client_id =c.id                

    ORDER BY `i`.`created_at` DESC 
    LIMIT 100 OFFSET 0

这是EXPLAIN (EDITED):

+----+-------------+-------+--------+--------------------+-----------+---------+------------------------+------+------------------------------+
| id | select_type | table | type   | possible_keys      | key       | key_len | ref                    | rows | Extra                        |
+----+-------------+-------+--------+--------------------+-----------+---------+------------------------+------+------------------------------+
|  1 | SIMPLE      | c     | index  | PRIMARY            | PRIMARY   | 4       | NULL                   |    1 | Using index; Using temporary |
|  1 | SIMPLE      | g     | ref    | PRIMARY,client_id  | client_id | 4       | clubr_new.c.id         |    3 | Using index                  |
|  1 | SIMPLE      | sg    | ref    | group_id,search_id | group_id  | 4       | clubr_new.g.id         |    1 | Using index                  |
|  1 | SIMPLE      | s     | eq_ref | PRIMARY            | PRIMARY   | 4       | clubr_new.sg.search_id |    1 | Using index                  |
|  1 | SIMPLE      | r     | ref    | search_id,item_id  | search_id | 4       | clubr_new.s.id         | 4359 | Using where                  |
|  1 | SIMPLE      | i     | eq_ref | PRIMARY            | PRIMARY   | 8       | clubr_new.r.item_id    |    1 |                              |
|  1 | SIMPLE      | u     | eq_ref | PRIMARY            | PRIMARY   | 8       | clubr_new.i.user_id    |    1 | Using index                  |
|  1 | SIMPLE      | t     | eq_ref | PRIMARY            | PRIMARY   | 4       | clubr_new.i.id         |    1 |                              |
|  1 | SIMPLE      | tu    | eq_ref | PRIMARY            | PRIMARY   | 8       | clubr_new.u.id         |    1 |                              |
+----+-------------+-------+--------+--------------------+-----------+---------+------------------------+------+------------------------------+

这是mtrt_items表格:

+--------------+-------------------------------------------------------+------+-----+---------+----------------+
| Field        | Type                                                  | Null | Key | Default | Extra          |
+--------------+-------------------------------------------------------+------+-----+---------+----------------+
| id           | bigint(20)                                            | NO   | PRI | NULL    | auto_increment |
| entity       | enum('twitter','facebook','youtube','flickr','orkut') | NO   | MUL | NULL    |                |
| user_id      | bigint(20)                                            | NO   | MUL | NULL    |                |
| created_at   | datetime                                              | NO   | MUL | NULL    |                |
| collected_at | datetime                                              | NO   |     | NULL    |                |
+--------------+-------------------------------------------------------+------+-----+---------+----------------+

 CREATE TABLE `mtrt_items` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `entity` enum('twitter','facebook','youtube','flickr','orkut') COLLATE utf8_unicode_ci NOT NULL,
  `user_id` bigint(20) NOT NULL,
  `created_at` datetime NOT NULL,
  `collected_at` datetime NOT NULL,
  PRIMARY KEY (`id`),
  KEY `mtrt_user_id` (`user_id`),
  KEY `entity` (`entity`),
  KEY `created_at` (`created_at`),
  CONSTRAINT `mtrt_items_ibfk_1` FOREIGN KEY (`user_id`) REFERENCES `mtrt_users` (`id`) ON DELETE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=309650 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci

的twt_tweets_content是MyISAM和也用于fulltext搜索:

+-----------+--------------+------+-----+---------+-------+
| Field     | Type         | Null | Key | Default | Extra |
+-----------+--------------+------+-----+---------+-------+
| id        | int(11)      | NO   | PRI | NULL    |       |
| user_id   | int(11)      | NO   | MUL | NULL    |       |
| status_id | varchar(100) | NO   | MUL | NULL    |       |
| content   | varchar(200) | NO   | MUL | NULL    |       |
+-----------+--------------+------+-----+---------+-------+

Answer 1

不要将其Order By放入主查询中,而是将其包装起来,如下所示:

SELECT * FROM (   
  ... your query
) ORDER BY `created at`

看一下查询计划.您将发现在您的情况下,在执行mtrt_items外部联接之前,会在您的表上执行排序.在我部分提供的重写中,排序在外连接之后应用,并应用于更小的集合.

UPDATE

假设LIMIT应用于大型集合(500,000？),看起来您可以在执行任何连接之前执行顶部.

SELECT * from (
    SELECT 
    `id`, ... `created_at`, ...
    ORDER BY `i`.`created_at` DESC 
    LIMIT 100 OFFSET 0) as i

    LEFT JOIN `mtrt_users` AS `u` ON i.user_id =u.id

    LEFT JOIN `twt_tweets_content` AS `t` ON t.id =i.id
    LEFT JOIN `twt_users` AS `tu` ON t.user_id = tu.id

    INNER JOIN `mtrt_items_searches` AS `r` ON i.id =r.item_id
    INNER JOIN `mtrt_searches` AS `s` ON s.id =r.search_id
    INNER JOIN `mtrt_searches_groups` AS `sg` ON sg.search_id =s.id
    INNER JOIN `mtrt_search_groups` AS `g` ON sg.group_id =g.id
    INNER JOIN `account_clients` AS `c` ON g.client_id =c.id                

GROUP BY i.id