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POOptimize MySql query: Too slow when ordering
 

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    <blockquote> <p>(edited) For more details about the app it self, please, also see: <a href="https://stackoverflow.com/questions/6785287/simple-but-heavy-application-consuming-a-lot-of-resources-how-to-optimize">Simple but heavy application consuming a lot of resources. How to Optimize?</a> (The adopted solution was use both joins and fulltext search)</p> </blockquote> <p>I have the following query running up to roughly 500.000 rows in 25 seconds. If I remove the ORDER, it takes 0.5 seconds.</p> <p><strong>Fisrt test</strong></p> <p>Keeping the <code>ORDER</code> and removing all t. and tu. columns, the query takes 7 seconds.</p> <p><strong>Second test</strong></p> <p>If I add or remove an INDEX to the i.created_at field the response time remain the same.</p> <p><strong>QUERY:</strong></p> <blockquote> <p>**EDITED: I'VE NOTICED THAT BOTH GROUP BY AND ORDER BY SLOW DOWN THE QUERY (I've also achieve a little gain in the query changing the joins. The gain was to 10secs, but at all, the problem remains). With the modification, the EXPLAIN have stopped to return filesort, but stills returning "using temporary" **</p> </blockquote> <pre><code>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 </code></pre> <p>Here is the <code>EXPLAIN</code> <strong>(EDITED)</strong>:</p> <pre><code>+----+-------------+-------+--------+--------------------+-----------+---------+------------------------+------+------------------------------+ | 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 | | +----+-------------+-------+--------+--------------------+-----------+---------+------------------------+------+------------------------------+ </code></pre> <p>Here is the <code>mtrt_items</code> table:</p> <pre><code>+--------------+-------------------------------------------------------+------+-----+---------+----------------+ | 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 </code></pre> <p>The <code>twt_tweets_content</code> is MyISAM and is also used for <code>fulltext</code> searches:</p> <pre><code>+-----------+--------------+------+-----+---------+-------+ | 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 | | +-----------+--------------+------+-----+---------+-------+ </code></pre>
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    1. COJust to be sure, you're doing RESET QUERY CACHE before each benchmark. right?
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    2. COwhat happens when you try `ORDER BY `i`.`id` DESC` ? Generally it would give you the exact same result. id is auto increment, so an older id means that the record was created further in the past.
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    3. CO@spinning_plate Actually, I use `SELECT SQL_NO_CACHE...`.
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