[英]How can I speed up a Group By statement with multiple Joins?
我在尝试加速查询时遇到的问题只有200万行,这个查询大约需要11秒。 这是我的sqlfiddle的链接 。 这是我试图运行的语句和我的EXPLAIN语句。
查询:
SELECT crawl.pk Pk,domains.domain Domain,
CONCAT(schemes.scheme, "://", domains.domain, remainders.remainder) Uri,
crawl.redirect Redirect FROM crawl
LEFT JOIN dates ON crawl.date_crawled=dates.pk
LEFT JOIN schemes ON crawl.scheme=schemes.pk
LEFT JOIN domains ON crawl.domain=domains.pk
LEFT JOIN remainders ON crawl.remainder=remainders.pk
WHERE (dates.date < CURDATE() - INTERVAL 30 DAY)
AND crawl.redirect=0
GROUP BY crawl.domain
ORDER BY crawl.date_crawled ASC
LIMIT 50
说明:
+----+-------------+------------+--------+-----------------------+-----------------------+---------+----------------------------+--------+----------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+------------+--------+-----------------------+-----------------------+---------+----------------------------+--------+----------------------------------------------+
| 1 | SIMPLE | dates | ALL | PRIMARY,date | NULL | NULL | NULL | 7 | Using where; Using temporary; Using filesort |
| 1 | SIMPLE | crawl | ref | date_crawled_redirect | date_crawled_redirect | 8 | mytable.dates.pk,const | 408644 | |
| 1 | SIMPLE | schemes | eq_ref | PRIMARY | PRIMARY | 4 | mytable.crawl.scheme | 1 | |
| 1 | SIMPLE | domains | eq_ref | PRIMARY | PRIMARY | 4 | mytable.crawl.domain | 1 | |
| 1 | SIMPLE | remainders | eq_ref | PRIMARY | PRIMARY | 4 | mytable.crawl.remainder | 1 | |
+----+-------------+------------+--------+-----------------------+-----------------------+---------+----------------------------+--------+----------------------------------------------+
5 rows in set (2.26 sec)
编辑#1:根据评论,我已经用连接替换了左连接,并通过连接移动了日期过滤器。 遗憾的是,这并没有减少查询时间。
SELECT crawl.pk Pk,domains.domain Domain, CONCAT(schemes.scheme, "://", domains.domain, remainders.remainder) Uri, crawl.redirect Redirect
FROM crawl
JOIN schemes ON crawl.scheme=schemes.pk
JOIN domains ON crawl.domain=domains.pk
JOIN remainders ON crawl.remainder=remainders.pk
JOIN dates ON crawl.date_crawled=dates.pk AND dates.date < CURDATE() - INTERVAL 30 DAY
WHERE crawl.redirect=0
GROUP BY crawl.domain
ORDER BY crawl.date_crawled ASC
LIMIT 50
编辑#2:我更新的说明:
+----+-------------+------------+--------+---------------------------------------------------------+-----------------------+---------+----------------------------+--------+-----------------------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+------------+--------+---------------------------------------------------------+-----------------------+---------+----------------------------+--------+-----------------------------------------------------------+
| 1 | SIMPLE | dates | range | PRIMARY,date,date_pk,dateBtreeIdx,pk | date_pk | 3 | NULL | 4 | Using where; Using index; Using temporary; Using filesort |
| 1 | SIMPLE | crawl | ref | domain_remainder,remainder,scheme,date_crawled_redirect | date_crawled_redirect | 8 | mytable.dates.pk,const | 408644 | |
| 1 | SIMPLE | schemes | ALL | PRIMARY | NULL | NULL | NULL | 2 | Using where; Using join buffer |
| 1 | SIMPLE | domains | eq_ref | PRIMARY | PRIMARY | 4 | mytable.crawl.domain | 1 | |
| 1 | SIMPLE | remainders | eq_ref | PRIMARY | PRIMARY | 4 | mytable.crawl.remainder | 1 | |
+----+-------------+------------+--------+---------------------------------------------------------+-----------------------+---------+----------------------------+--------+-----------------------------------------------------------+
编辑#3
+----+--------------------+------------+-----------------+------------------------------------------+---------+---------+----------------------------+---------+---------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+--------------------+------------+-----------------+------------------------------------------+---------+---------+----------------------------+---------+---------------------------------+
| 1 | PRIMARY | schemes | ALL | PRIMARY | NULL | NULL | NULL | 2 | Using temporary; Using filesort |
| 1 | PRIMARY | crawl | ref | domain_remainder,remainder,scheme,domain | scheme | 4 | mytable.schemes.pk | 1448223 | Using where |
| 1 | PRIMARY | domains | eq_ref | PRIMARY | PRIMARY | 4 | mytable.crawl.domain | 1 | |
| 1 | PRIMARY | remainders | eq_ref | PRIMARY | PRIMARY | 4 | mytable.crawl.remainder | 1 | |
| 2 | DEPENDENT SUBQUERY | dates | unique_subquery | PRIMARY,date,date_pk,dateBtreeIdx,pk | PRIMARY | 4 | func | 1 | Using where |
+----+--------------------+------------+-----------------+------------------------------------------+---------+---------+----------------------------+---------+---------------------------------+
5 rows in set (0.04 sec)
编辑#4:
+----+-------------+------------+--------+--------------------------------------+-------------------------+---------+----------------------------+---------+-----------------------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+------------+--------+--------------------------------------+-------------------------+---------+----------------------------+---------+-----------------------------------------------------------+
| 1 | SIMPLE | dates | range | PRIMARY,date,date_pk,dateBtreeIdx,pk | date_pk | 3 | NULL | 4 | Using where; Using index; Using temporary; Using filesort |
| 1 | SIMPLE | schemes | ALL | PRIMARY | NULL | NULL | NULL | 2 | Using join buffer |
| 1 | SIMPLE | crawl | ref | scheme_domain_remainder | scheme_domain_remainder | 4 | mytable.schemes.pk | 1455517 | Using where |
| 1 | SIMPLE | domains | eq_ref | PRIMARY | PRIMARY | 4 | mytable.crawl.domain | 1 | |
| 1 | SIMPLE | remainders | eq_ref | PRIMARY | PRIMARY | 4 | mytable.crawl.remainder | 1 | |
+----+-------------+------------+--------+--------------------------------------+-------------------------+---------+----------------------------+---------+-----------------------------------------------------------+
5 rows in set (0.04 sec)
编辑#5
SELECT urls.pk PK, domains.domain Domain, CONCAT(schemes.scheme, "://", domains.domain, remainders.remainder) Uri, urls.redirect Redirect, urls.date_crawled DC FROM
(SELECT * FROM (
SELECT * FROM crawl as urls ORDER BY date_crawled ASC
) AS tmp GROUP BY tmp.domain ) as urls
JOIN schemes ON urls.scheme=schemes.pk
JOIN domains ON urls.domain=domains.pk
JOIN remainders ON urls.remainder=remainders.pk
JOIN dates ON urls.date_crawled=dates.pk AND dates.date < CURDATE() - INTERVAL 30 DAY
WHERE urls.redirect=0
ORDER BY urls.date_crawled ASC
LIMIT 50
您手头有一个近乎理想的查询。 唯一的问题是表格dates
非最佳索引。 正如您在EXPLAIN
输出中看到的,MySQL无法在表dates
使用任何索引,因此它将用作第一个表。 这会导致表crawl
的半优化执行计划,并且需要访问大量的行。
要改善这一点,您应该在dates.date
列上添加BTREE
索引:
ALTER TABLE dates ADD INDEX dateBtreeIdx USING BTREE (date)
BTREE指数用于范围条件。 在你的情况下,“低于”, 见这里 。
基于此,您可以尝试将join-field Dates.pk
添加到索引中。 这可能会进一步加快查询速度,但取决于您的数据。
编辑
现在MySQL可以在date.dates
上使用Index(type = RANGE和rows = 4)。 你没有看到加速,因为现在优化器不会在schemes
使用PRIMARY KEY
...
但最大的性能,问题与保持crawl
。 尝试使用IN
查询的其他方法:
SELECT
crawl.pk Pk, domains.domain Domain,
CONCAT(schemes.scheme, "://", domains.domain, remainders.remainder) Uri,
crawl.redirect Redirect
FROM
crawl, schemes, domains, remainders
WHERE
crawl.scheme=schemes.pk
AND crawl.domain=domains.pk
AND crawl.remainder=remainders.pk
AND crawl.date_crawled IN (SELECT pk FROM dates WHERE (dates.date < CURDATE() - INTERVAL 30 DAY))
AND crawl.redirect=0
GROUP BY
crawl.domain
ORDER BY
crawl.date_crawled ASC
LIMIT 50
编辑#2
SELECT
urls.pk PK, domains.domain Domain,
CONCAT(schemes.scheme, "://", domains.domain, remainders.remainder) Uri,
urls.redirect Redirect,
urls.date_crawled DC
FROM
(SELECT pk, redirect, date_crawled FROM crawl GROUP BY `domain` ) as urls
JOIN schemes ON urls.scheme=schemes.pk
JOIN domains ON urls.`domain`=domains.pk
JOIN remainders ON urls.remainder=remainders.pk
JOIN dates ON urls.date_crawled=dates.pk AND dates.date < CURDATE() - INTERVAL 30 DAY
WHERE
urls.redirect=0
ORDER BY urls.date_crawled ASC
LIMIT 50
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