Question

最近我有了这个question，一切正常，直到我把它发送到DreamHost的服务器。

下面的查询似乎花了很长时间才执行，我无法弄清楚为什么一次处理这么多行。在我的本地服务器中，在0.3秒内执行了相同的查询。

SELECT feed_entries . *
FROM feed_entries
WHERE 
id
IN (

SELECT e.id
FROM feed_entries AS e
INNER JOIN feeds AS f ON e.feed_id = f.id
INNER JOIN entries_categorias AS ec ON ec.entry_id = e.id
INNER JOIN categorias AS c ON ec.categoria_id = c.id
WHERE 
e.deleted =0
AND 
c.slug
IN ('entenda', 'google')
GROUP BY e.id
HAVING COUNT( DISTINCT ec.id ) =2

)
ORDER BY date DESC
LIMIT 1

这是我从支持团队收到的消息：

好吧，它看起来像是查询由于这些其他查询而被锁定像这一样，加工650万记录，持续11秒。

# Query_time: 11.639269  Lock_time: 0.000192 Rows_sent: 2  Rows_examined:
6509098
use desenvolvimentistas;
SET timestamp=1280325753;
SELECT `e`.*, `f`.`titulo` AS `feedTitulo`, `f`.`url` AS `feedUrl` FROM
`feed_entries` AS `e`
 INNER JOIN `feeds` AS `f` ON e.feed_id =f.id WHERE (e.id IN (SELECT
`e`.`id` FROM `feed_entries` AS `e`
 INNER JOIN `feeds` AS `f` ON e.feed_id =f.id
 INNER JOIN `entries_categorias` AS `ec` ON ec.entry_id =e.id
 INNER JOIN `categorias` AS `c` ON ec.categoria_id =c.id WHERE (e.deleted
=0) AND (e.id NOT IN ('', '', '842', '853', '774', '878')) AND
(e.imagem145x145 =1) AND (c.slug IN('destaque-2')) GROUP BY `e`.`id`
HAVING (COUNT(DISTINCT ec.id) =1))) ORDER BY `e`.`date` DESC LIMIT 4;

可能查询需要0.3秒   在您的本地计算机上运行   闲置，但我们的服务器速度很慢   因为它正在运行查询150   一个时间，每个人都在处理   1530万条记录。

我让我们的mysql管理员看了一下   它和他说这是相当的   效率低下并且感到惊讶   数据库甚至可访问，因为   这些查询已被锁定。他   如果说，数据库将被禁用   它继续这种方式和原因   服务器问题。他说你应该   修复检查的行或获取MySQL   PS，虽然mysql ps不会修复   它，但反而只会阻止   数据库被禁用。

以下是查询：

# Query_time: 25.944779  Lock_time: 0.000176 Rows_sent: 0  Rows_examined:
15378209
use desenvolvimentistas;
SELECT `feed_entries`.* FROM `feed_entries` WHERE (id IN (SELECT `e`.`id`
FROM `feed_entries` AS `e` INNER JOIN `feeds` AS `f` ON e.feed_id =f.id
INNER JOIN `entries_categorias` AS `ec` ON ec.entry_id =e.id INNER JOIN
`categorias` AS `c` ON ec.categoria_id =c.id WHERE (e.deleted =0) AND
(c.slug IN('entenda','google')) GROUP BY `e`.`id` HAVING (COUNT(DISTINCT
ec.id) =2))) ORDER BY `date` DESC LIMIT 1;

这是另一个需要修复的问题：

# Query_time: 27.010857  Lock_time: 0.000165 Rows_sent: 0  Rows_examined:
15382750
use desenvolvimentistas;
SET timestamp=1280325706;
SELECT `e`.*, `f`.`titulo` AS `feedTitulo`, `f`.`url` AS `feedUrl` FROM
`feed_entries` AS `e`
 INNER JOIN `feeds` AS `f` ON e.feed_id =f.id WHERE (e.id IN (SELECT
`e`.`id` FROM `feed_entries` AS `e`
 INNER JOIN `feeds` AS `f` ON e.feed_id =f.id
 INNER JOIN `entries_categorias` AS `ec` ON ec.entry_id =e.id
 INNER JOIN `categorias` AS `c` ON ec.categoria_id =c.id WHERE (e.deleted
=0) AND (c.slug IN('manchete', 'google')) GROUP BY `e`.`id` HAVING
(COUNT(DISTINCT ec.id) =2))) ORDER BY `e`.`date` DESC LIMIT 4;7:18

Answer 1

我要检查的第一件事是托管服务器上有正确的索引。有时，人们在迁移数据库时忘记移动它们。

Answer 2

你总是可以缓存它; - ）

Answer 3

理想情况下，每个问题需要一个查询 - 您可以提出的问题数量没有限制，并且可以最大限度地减少与每个查询相关的聊天。

我将您的第一个查询重写为：

  SELECT t.*
    FROM feed_entries t
   WHERE EXISTS(SELECT NULL
                  FROM feed_entries AS e
                  JOIN feeds AS f ON e.feed_id = f.id
                  JOIN entries_categorias AS ec ON ec.entry_id = e.id
                  JOIN categorias AS c ON ec.categoria_id = c.id
                 WHERE e.deleted = 0
                   AND c.slug IN ('entenda', 'google')
                   AND e.id = t.id
              GROUP BY e.id
                HAVING COUNT( DISTINCT ec.id ) = 2)
ORDER BY date DESC
   LIMIT 1

将JOIN条件中使用的列至少编入索引（如果还没有）。

我看到有关查询运行150次的评论 - 你能详细说明一下吗？

Answer 4

我尝试从内部查询中创建一个查询。然后手动将结果id添加到外部on（其中id为（1,2,3,4,5））。虽然这不会自动提高性能，但您至少知道发生了什么。

他们描述问题的方式，甚至可能是对从外循环检查的每个单个记录测试内循环，这将通过这种方法来修复。虽然我认为MySQL足够聪明不能自己解决这个问题。

如何提高此查询的性能？

4 个答案: