非常慢的MySql查詢Joomla 2.5

Question

我的網站遇到非常緩慢的查詢，例如以下查詢。 是Joomla 2.5。

# Query_time: 19.797091  Lock_time: 0.000561 Rows_sent: 12  Rows_examined: 4127
SET timestamp=1385467501;
SELECT a.fulltext, a.id, a.title, a.alias, a.title_alias, a.introtext, a.state, a.catid, a.created, a.created_by, a.created_by_alias,a.images, a.modified, a.modified_by,a.publish_up, a.publish_down, a.attribs, a.metadata, a.metakey, a.metadesc, a.access, a.hits, a.featured, LENGTH(a.fulltext) AS readmore,a.fulltext, a.id, a.title, a.alias, a.title_alias, a.introtext, a.state, a.catid, a.created, a.created_by, a.created_by_alias,a.images, a.modified, a.modified_by,a.publish_up, a.publish_down, a.attribs, a.metadata, a.metakey, a.metadesc, a.access, a.hits, a.featured, LENGTH(a.fulltext) AS readmore,c.title AS category_title, c.path AS category_route, c.access AS category_access, c.alias AS category_alias,CASE WHEN a.created_by_alias > ' ' THEN a.created_by_alias ELSE ua.name END AS author,ua.email AS author_email,contact.id as contactid,parent.title as parent_title, parent.id as parent_id, parent.path as parent_route, parent.alias as parent_alias,ROUND(v.rating_sum / v.rating_count, 0) AS rating, v.rating_count as rating_count,c.published, CASE WHEN badcats.id is null THEN c.published ELSE 0 END AS parents_published
FROM j25_content AS a
LEFT JOIN j25_content_frontpage AS fp ON fp.content_id = a.id
LEFT JOIN j25_categories AS c ON c.id = a.catid
LEFT JOIN j25_users AS ua ON ua.id = a.created_by
LEFT JOIN j25_users AS uam ON uam.id = a.modified_by
LEFT JOIN (
SELECT contact.user_id, MAX(contact.id) AS id, contact.language
FROM j25_contact_details AS contact
WHERE contact.published = 1
GROUP BY contact.user_id, contact.language) AS contact ON contact.user_id = a.created_by
LEFT JOIN j25_categories as parent ON parent.id = c.parent_id
LEFT JOIN j25_content_rating AS v ON a.id = v.content_id
LEFT OUTER JOIN (SELECT cat.id as id FROM j25_categories AS cat JOIN j25_categories AS parent ON cat.lft BETWEEN parent.lft AND parent.rgt WHERE parent.extension = 'com_content' AND parent.published != 1 GROUP BY cat.id ) AS badcats ON badcats.id = c.id
WHERE a.access IN (1,1) AND c.access IN (1,1) AND CASE WHEN badcats.id is null THEN a.state ELSE 0 END = 1 AND a.featured = 0 AND a.catid IN (181,89,173,174,49,128,124,175,129,133,121,176,135,180,177,178,179,90) AND (a.publish_up = '0000-00-00 00:00:00' OR a.publish_up <= '2013-11-26 12:04:24') AND (a.publish_down = '0000-00-00 00:00:00' OR a.publish_down >= '2013-11-26 12:04:24')
GROUP BY a.id, a.title, a.alias, a.title_alias, a.introtext, a.checked_out, a.checked_out_time, a.catid, a.created, a.created_by, a.created_by_alias, a.created, a.modified, a.modified_by, uam.name, a.publish_up, a.attribs, a.metadata, a.metakey, a.metadesc, a.access, a.hits, a.xreference, a.featured, a.fulltext, a.state, a.publish_down, badcats.id, c.title, c.path, c.access, c.alias, uam.id, ua.name, ua.email, contact.id, parent.title, parent.id, parent.path, parent.alias, v.rating_sum, v.rating_count, c.published, c.lft, a.ordering, parent.lft, fp.ordering, c.id, a.images, a.urls
ORDER BY a.created DESC LIMIT 0, 12;

我該怎么做才能加快速度？ 這些表中的一些索引會有所幫助嗎？ 謝謝。

Answer 1

絕對索引有助於查詢。 而且，我認為您的輔助查找參考表（類別，用戶，內容分級等）中的每個表都應在MINIMUM處有一個索引，以指示表之間的聯接條件。

table                 index on
j25_content           ( access, featured, catid, publish_up, publish_down, state, id, created_by, modified_by )
j25_content_frontpage ( content_id )
j25_categories        ( id, parent_id )
ANOTHER index...
j25_categories        ( extension, published, lft, rgt, id )
j25_users             ( id )
j25_contact_details   ( published, user_id, language, id )
j25_content_rating    ( content_id )

我將這些索引設置為“覆蓋”索引……這意味着它們應通過將所有字段作為索引的一部分來幫助優化查詢，因此不必轉到原始數據頁即可查看是否所有作品都有資格返回記錄

首先嘗試...

我要嘗試的下一個方法是MySQL具有一個特殊的關鍵字“ STRAIGHT_JOIN”，該關鍵字告訴引擎按照您指定的順序運行查詢。 您似乎有很好的表基礎作為主表，而查找表則作為輔助表。 引擎可能正在嘗試為您考慮並使用較小的表之一來運行查詢。

select STRAIGHT_JOIN  (rest of your query exactly as it is)