[英]MySQL specific query performance tuning
我的MySQL查詢性能有問題。
表(InnoDB):
+--------------------+---------------------+------+-----+-------------------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------------------+---------------------+------+-----+-------------------+-------+
| st_resource_id | varchar(32) | NO | MUL | NULL | |
| st_sub_resource_id | varchar(32) | YES | | NULL | |
| st_title | varchar(500) | YES | | NULL | |
| st_resource_type | varchar(100) | NO | MUL | NULL | |
| st_site_id | tinyint(4) | NO | MUL | NULL | |
| st_time | timestamp | NO | MUL | CURRENT_TIMESTAMP | |
| st_user_id | int(10) unsigned | YES | | NULL | |
| st_full_access | tinyint(1) unsigned | YES | | NULL | |
+--------------------+---------------------+------+-----+-------------------+-------+
索引:
+---------------+------------+------------------+--------------+--------------------+-----------+-------------+----------+--------+------+------------+---------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+---------------+------------+------------------+--------------+--------------------+-----------+-------------+----------+--------+------+------------+---------+
| nr_statistics | 1 | resource_id | 1 | st_resource_id | A | 1546165 | NULL | NULL | | BTREE | |
| nr_statistics | 1 | resource_id | 2 | st_sub_resource_id | A | 1546165 | NULL | NULL | YES | BTREE | |
| nr_statistics | 1 | st_time | 1 | st_time | A | 1546165 | NULL | NULL | | BTREE | |
| nr_statistics | 1 | st_site_id | 1 | st_site_id | A | 16 | NULL | NULL | | BTREE | |
| nr_statistics | 1 | st_resource_type | 1 | st_resource_type | A | 16 | 10 | NULL | | BTREE | |
+---------------+------------+------------------+--------------+--------------------+-----------+-------------+----------+--------+------+------------+---------+
查詢:
SELECT st_resource_id AS docId, count(*) AS cnt
FROM nr_statistics
WHERE
st_resource_type = 'document'
AND st_sub_resource_id = 'text'
AND st_time > DATE_SUB(NOW(), INTERVAL 7 DAY)
AND st_site_id = 1
GROUP BY st_resource_id
ORDER BY cnt DESC
LIMIT 0, 5;
查詢計划:
+----+-------------+---------------+-------+-------------------------------------+-------------+---------+------+---------+----------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+---------------+-------+-------------------------------------+-------------+---------+------+---------+----------------------------------------------+
| 1 | SIMPLE | nr_statistics | index | st_time,st_site_id,st_resource_type | resource_id | 197 | NULL | 1581044 | Using where; Using temporary; Using filesort |
+----+-------------+---------------+-------+-------------------------------------+-------------+---------+------+---------+----------------------------------------------+
表有~1,666,383行。 查詢運行速度非常慢。 在MySQL進程列表中,我在“復制到tmp表階段”中看到這個查詢很長一段時間(> 1分鍾)。 查詢會產生大量I / O負載。 我無法理解如何解決問題並加快查詢執行速度。
如果問題是錯誤索引的結果,那么哪些索引會正確?
UPD。 我創建了新的復合索引:
| nr_statistics | 1 | st_site_id_2 | 1 | st_site_id | A | 16 | NULL | NULL | | BTREE | |
| nr_statistics | 1 | st_site_id_2 | 2 | st_resource_type | A | 16 | NULL | NULL | | BTREE | |
| nr_statistics | 1 | st_site_id_2 | 3 | st_sub_resource_id | A | 752018 | NULL | NULL | YES | BTREE | |
| nr_statistics | 1 | st_site_id_2 | 4 | st_time | A | 1504037 | NULL | NULL | | BTREE | |
| nr_statistics | 1 | st_site_id_2 | 5 | st_resource_id | A | 1504037 | NULL | NULL | | BTREE | |
現在查詢計划是:
+----+-------------+---------------+-------+---------------+--------------+---------+------+-------+-----------------------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+---------------+-------+---------------+--------------+---------+------+-------+-----------------------------------------------------------+
| 1 | SIMPLE | nr_statistics | range | st_site_id_2 | st_site_id_2 | 406 | NULL | 21168 | Using where; Using index; Using temporary; Using filesort |
+----+-------------+---------------+-------+---------------+--------------+---------+------+-------+-----------------------------------------------------------+
查詢現在運行速度非常快(為0.0x秒),但我必須強制使用新索引:
SELECT st_resource_id as docId, count( * ) AS Cnt
FROM nr_statistics
USE INDEX (st_site_id_2)
WHERE st_resource_type = 'document'
AND st_sub_resource_id = 'text'
AND st_time > DATE_SUB( NOW( ) , INTERVAL 7 DAY )
AND st_site_id = 1
GROUP BY st_resource_id
ORDER BY cnt DESC
LIMIT 0 , 5;
雖然問題得到了解決(不是很漂亮但有效的方式),但我仍然有一些懸而未決的問題(見評論)。
在(st_site_id, st_resource_type, st_sub_resourse_id, st_time, st_resource_id)
上創建復合索引。
但是,你仍然有temporary
和filesort
的計划,因為您訂購的COUNT(*)
這是不可轉位。
如果您需要快速且經常地運行此查詢,則必須創建一個聚合表,該表將存儲每個站點/資源/子課程/周組合的計數,並在觸發器中更新它。
您是否嘗試在st_resource_type, st_resource_id, st_time and st_site_id
上創建復合索引? 它看起來像你有幾個索引,但大多數是在一列,或可能是2列。 通過使用您需要的更多列的復合索引,可以提高性能。
在使用多個where子句進行查詢時,編寫它們的順序應與編寫查詢的順序相匹配。
在您的特定情況下,它將是:
CREATE INDEX stats_index ON nr_statistics (st_resource_type, st_sub_resource_id, st_time, st_site_id);
這應該會給你一個非常好的速度提升。
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.