需要帮助调优sql查询

Question

我的mysql数据库已经变得CPU饥饿,试图执行一个特别慢的查询.当我做一个解释时,mysql说"使用where;使用临时;使用filesort".请帮助解密和解决这个难题.

表结构:

CREATE TABLE `topsources` (
  `USER_ID` varchar(255) NOT NULL,
   `UPDATED_TIME` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
  `URL_ID` int(11) NOT NULL,
  `SOURCE_SLUG` varchar(100) NOT NULL,
  `FEED_PAGE_URL` varchar(255) NOT NULL,
  `CATEGORY_SLUG` varchar(100) NOT NULL,
  `REFERRER` varchar(2048) DEFAULT NULL,
  PRIMARY KEY (`USER_ID`,`URL_ID`),
  KEY `USER_ID` (`USER_ID`),
  KEY `FEED_PAGE_URL` (`FEED_PAGE_URL`),
  KEY `SOURCE_SLUG` (`SOURCE_SLUG`),
  KEY `CATEGORY_SLUG` (`CATEGORY_SLUG`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;

该表有370K行...有时更高.以下查询需要10秒以上.

SELECT topsources.SOURCE_SLUG, COUNT(topsources.SOURCE_SLUG) AS VIEW_COUNT
FROM topsources
WHERE CATEGORY_SLUG = '/newssource'
GROUP BY topsources.SOURCE_SLUG
HAVING MAX(CASE WHEN topsources.USER_ID = 'xxxx' THEN 1 ELSE 0 END) = 0
ORDER BY VIEW_COUNT DESC;

这是扩展说明:

+----+-------------+------------+------+---------------+---------------+---------+-------+--------+----------+----------------------------------------------+
| id | select_type | table      | type | possible_keys | key           | key_len | ref   | rows   | filtered | Extra                                        |
+----+-------------+------------+------+---------------+---------------+---------+-------+--------+----------+----------------------------------------------+
|  1 | SIMPLE      | topsources | ref  | CATEGORY_SLUG | CATEGORY_SLUG | 302     | const | 160790 |   100.00 | Using where; Using temporary; Using filesort |
+----+-------------+------------+------+---------------+----

----------- --------- + ------- + -------- + + ---------- + ---------------------------------------------- +

有没有办法改善这个查询？此外,是否有任何mysql设置可以帮助减少CPU负载？我可以分配更多可在我的服务器上使用的内存.

Answer 1

如果我正确地阅读了我的 sql 更改，这应该可以解决问题

SELECT topsources.SOURCE_SLUG, COUNT(topsources.SOURCE_SLUG) AS VIEW_COUNT
FROM topsources
WHERE CATEGORY_SLUG = '/newssource' and 
    topsources.SOURCE_SLUG not in (
        select distinct SOURCE_SLUG 
        from topsources 
        where USER_ID = 'xxxx'
        )
GROUP BY topsources.SOURCE_SLUG
ORDER BY VIEW_COUNT DESC;