私はいくつかのクエリを最適化しようと取り組んでおり、不可解な結果が得られています (おそらく、MySQL の内部動作についての私の理解が限られていることに起因します)。
不可解なことは (少なくともこの時点で)、完全なクエリを分析して最適化しようとしたときに、内部の選択クエリ (サブクエリ) が単独ではるかに遅く実行されることがわかったことです。単純なクエリの方が高速に実行されると思いました。以下は、クエリと私の結果です。
完全なクエリ
SELECT r.id, r.serve_url, r.title, r.category_id, GROUP_CONCAT(hr.server_id) AS server_id
FROM hosted_resources hr
LEFT JOIN resources AS r ON (hr.resource_id = r.id)
WHERE hr.resource_id = (
select id from resources
where resource_type_id = 1
and category_id = 1
and id < 311
order by date_added desc
limit 1
)
GROUP BY r.id, r.serve_url, r.title, r.category_id;
EXPLAIN クエリの結果:
+----+-------------+-----------+-------+-------------------------------------------------------------------------------+----------------------------------------------+---------+-------+------+-----------------------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-----------+-------+-------------------------------------------------------------------------------+----------------------------------------------+---------+-------+------+-----------------------------------------------------------+
| 1 | PRIMARY | hr | ref | hosted_resources_resource_id_resource_id_idx,hosted_resources_resource_id_idx | hosted_resources_resource_id_resource_id_idx | 4 | const | 2 | Using where; Using index; Using temporary; Using filesort |
| 1 | PRIMARY | r | const | PRIMARY | PRIMARY | 4 | const | 1 | |
| 2 | SUBQUERY | resources | ref | PRIMARY,type_idx,category_idx,type_category_idx,type_category_date_idx | type_category_date_idx | 8 | | 87 | Using where; Using index |
+----+-------------+-----------+-------+-------------------------------------------------------------------------------+----------------------------------------------+---------+-------+------+-----------------------------------------------------------+
ベンチマーク結果:
Concurrency Level: 5000
Time taken for tests: 9.396 seconds
Complete requests: 100000
Failed requests: 0
Write errors: 0
Non-2xx responses: 100000
Total transferred: 31900000 bytes
HTML transferred: 16900000 bytes
Requests per second: 10642.78 [#/sec] (mean)
Time per request: 469.802 [ms] (mean)
Time per request: 0.094 [ms] (mean, across all concurrent requests)
Transfer rate: 3315.47 [Kbytes/sec] received
サブクエリ（より高速に実行されると予想していた）
select id, serve_url, title, category_id from resources
where resource_type_id = 1
and category_id = 1
and id < 311
order by date_added desc
limit 1
EXPLAIN クエリの結果:
+----+-------------+-----------+------+------------------------------------------------------------------------+------------------------+---------+-------------+------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-----------+------+------------------------------------------------------------------------+------------------------+---------+-------------+------+-------------+
| 1 | SIMPLE | resources | ref | PRIMARY,type_idx,category_idx,type_category_idx,type_category_date_idx | type_category_date_idx | 8 | const,const | 87 | Using where |
+----+-------------+-----------+------+------------------------------------------------------------------------+------------------------+---------+-------------+------+-------------+
ベンチマーク結果:
Concurrency Level: 5000
Time taken for tests: 42.181 seconds
Complete requests: 100000
Failed requests: 0
Write errors: 0
Total transferred: 41800000 bytes
HTML transferred: 27100000 bytes
Requests per second: 2370.75 [#/sec] (mean)
Time per request: 2109.040 [ms] (mean)
Time per request: 0.422 [ms] (mean, across all concurrent requests)
Transfer rate: 967.75 [Kbytes/sec] received
リソース テーブル:
CREATE TABLE `resources` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`date_added` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT
`resource_type_id` int(11) NOT NULL COMMENT,
`resource_status_id` int(11) NOT NULL COMMENT
`is_hosted` bit(1) NOT NULL COMMENT
`category_id` int(11) NOT NULL COMMENT
`serve_url` varchar(255) DEFAULT NULL COMMENT
`title` varchar(255) DEFAULT NULL COMMENT
`parent_resource_id` int(11) DEFAULT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `serve_url_UNIQUE` (`serve_url`),
KEY `type_idx` (`resource_type_id`),
KEY `status_idx` (`resource_status_id`),
KEY `category_idx` (`category_id`),
KEY `resources_parent_resource_id_idx` (`parent_resource_id`),
KEY `type_category_idx` (`resource_type_id`,`category_id`),
KEY `date_added_idx` (`date_added`),
KEY `type_category_date_idx` (`resource_type_id`,`category_id`,`date_added`),
CONSTRAINT `resources_category_id` FOREIGN KEY (`category_id`) REFERENCES `categories` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION,
CONSTRAINT `resources_parent_resource_id` FOREIGN KEY (`parent_resource_id`) REFERENCES `resources` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
CONSTRAINT `resources_resource_status_id` FOREIGN KEY (`resource_status_id`) REFERENCES `resource_statuses` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION,
CONSTRAINT `resources_resource_type_id` FOREIGN KEY (`resource_type_id`) REFERENCES `resource_types` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION
) ENGINE=InnoDB AUTO_INCREMENT=598 DEFAULT CHARSET=latin1;
どんな厳しいことでも大歓迎です。ケイト