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我正在使用 Industrialthemes 的 WordPress 主题引擎，并且看到首页的渲染使用了很多查询，这些查询在我的 MySQL 数据库中运行大约需要 0.4 秒。像这个：

SELECT SQL_NO_CACHE SQL_CALC_FOUND_ROWS wp_posts.ID
FROM wp_posts
INNER JOIN wp_term_relationships ON (wp_posts.ID = wp_term_relationships.object_id)
WHERE 1 =1
  AND (wp_term_relationships.term_taxonomy_id IN (1))
  AND wp_posts.post_type = 'post'
  AND (wp_posts.post_status = 'publish'
       OR wp_posts.post_status = 'closed')
GROUP BY wp_posts.ID
ORDER BY wp_posts.post_date DESC 
LIMIT 0,  5;

有什么办法可以改进这个查询？据我所知，WordPress 安装为所有涉及的字段设置了默认索引。我在调优 SQL Select 语句方面的知识并不好，所以我希望一些专家能在这方面帮助我。谢谢。

（来自评论）

CREATE TABLE wp_term_relationships (
    object_id bigint(20) unsigned NOT NULL DEFAULT '0', 
    term_taxonomy_id bigint(20) unsigned NOT NULL DEFAULT '0', 
    term_order int(11) NOT NULL DEFAULT '0', 
    PRIMARY KEY (object_id,term_taxonomy_id), 
    KEY term_taxonomy_id (term_taxonomy_id), 
    KEY idx1 (object_id)
) ENGINE=MyISAM DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci

（之后...）

CREATE TABLE wp_term_relationships (
    object_id bigint(20) unsigned NOT NULL DEFAULT '0', 
    term_taxonomy_id bigint(20) unsigned NOT NULL DEFAULT '0', 
    term_order int(11) NOT NULL DEFAULT '0', 
    PRIMARY KEY (object_id,term_taxonomy_id), 
    KEY term_taxonomy_id (term_taxonomy_id), 
    KEY idx1 (term_taxonomy_id,object_id)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci
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1 回答 1

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wp_term_relationships needs INDEX(term_taxonomy_id, object_id) -- in this order
wp_posts might benefit from INDEX(post_type, ID, post_status, post_date) -- in this order

Both are "covering" indexes.
The former lets the JOIN work efficiently and gives the optimizer the option of starting with wp_term_relationships. And it should replace KEY term_taxonomy_id (term_taxonomy_id).
The latter should work well regardless of which table is picked first.

(More)

SELECT  SQL_NO_CACHE SQL_CALC_FOUND_ROWS p.ID
    FROM  wp_posts AS p
     WHERE p.post_type = 'post'
      AND  p.post_status IN ( 'publish', 'closed' )
      AND EXISTS ( SELECT 1 FROM wp_term_relationships AS tr
                     WHERE p.ID = tr.object_id
                       AND tr.term_taxonomy_id IN (1) )
    ORDER BY  p.post_date DESC
    LIMIT  0, 5;

With this formulation,

If the EXPLAIN starts with p:

p:  (post_date, post_type, post_status, ID)
p:  (post_type, post_status, ID, post_date)
tr:  (object_id, term_taxonomy_id)  -- which you have

If the EXPLAIN starts with tr:

p:  (ID)  -- which you probably have
tr:  (term_taxonomy_id, object_id)

The main problems:

  • The GROUP BY was adding effort. (I eliminated it by changing the JOIN to an EXISTS.)
  • IN ( 'publish', 'closed' ) -- inhibits effective use of index.
  • SQL_CALC_FOUND_ROWS -- means that it can't stop when it gets 5 rows.
  • IN (1) turn into = 1, which is fine; but IN (1,2) is messier.

Or, to be more blunt, WP has not yet been engineered to scale.

Please add the indexes and get the EXPLAIN SELECT.

From pastebin:

SELECT  SQL_NO_CACHE p.ID
    FROM  wp_posts AS p
    WHERE  p.post_type = 'post'
      AND  p.post_status = 'publish'
      AND  EXISTS 
    (
        SELECT  1
            FROM  wp_term_relationships AS tr
            WHERE  p.ID = tr.object_id
              AND  EXISTS 
            (
                SELECT  1
                    from  wp_term_taxonomy AS tt
                    WHERE  tr.term_taxonomy_id = tt.term_taxonomy_id
                      AND  tt.taxonomy = 'post_tag'
                      AND  tt.term_id IN (548, 669) ) 
    );

This is a different query. It needs this also:

tt:  INDEX(term_taxonomy_id, taxonomy,  -- in either order
           term_id)   -- last

And...

SELECT  SQL_NO_CACHE wp_posts.ID
    FROM  wp_posts
    INNER JOIN  wp_term_relationships tr 
           ON (wp_posts.ID = tr.object_id)
    INNER JOIN  wp_term_taxonomy tt
           ON (tr.term_taxonomy_id = tt.term_taxonomy_id)
    WHERE  ( post_type = 'post'
              AND  post_status = 'publish'
              AND  tt.taxonomy = 'post_tag'
              AND  tt.term_id IN (548, 669)  
           )
    GROUP BY  wp_posts.ID;

needs

tt:  INDEX(taxonomy, term_id, term_taxonomy_id)  -- in this order

I would add both of those indexes to tt and see what happens to the EXPLAINs and to performance.

Rewrite query See if this gives you the 'right' answer:

SELECT  p.ID, p.post_name, p.post_title,
        p.post_type, p.post_status,
        tt.term_id as termid, tt.taxonomy
    FROM  wp_posts AS p
    INNER JOIN  wp_term_relationships tr  ON (p.ID = tr.object_id)
    INNER JOIN  wp_term_taxonomy tt  ON (tr.term_taxonomy_id = tt.term_taxonomy_id)
    WHERE  p.post_type = 'post'
      AND  p.post_status = 'publish'
      AND  tt.taxonomy = 'post_tag'
      AND  tt.term_id IN (548, 669)
    ORDER BY  p.ID;

Notes:

  • GROUP BY removed
  • AND/OR probably not working as expected: a AND b OR c is equivalent to (a AND b) OR c, but I think you wanted a AND (b OR c)
  • Did you add the recommended indexes?
于 2016-01-28T02:23:51.943 回答