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 程式師世界 >> 數據庫知識 >> MYSQL數據庫 >> 關於MYSQL數據庫 >> Mysql數據庫之索引優化

Mysql數據庫之索引優化

編輯:關於MYSQL數據庫

MySQL憑借著出色的性能、低廉的成本、豐富的資源,已經成為絕大多數互聯網公司的首選關系型數據庫。雖然性能出色,但所謂“好馬配好鞍”,如何能夠更好的使用它,已經成為開發工程師的必修課,我們經常會從職位描述上看到諸如“精通MySQL”、“SQL語句優化”、“了解數據庫原理”等要求。我們知道一般的應用系統,讀寫比例在10:1左右,而且插入操作和一般的更新操作很少出現性能問題,遇到最多的,也是最容易出問題的,還是一些復雜的查詢操作,所以查詢語句的優化顯然是重中之重。

問題:cpu負載過高,達到36。


現象:通過mysqladmin -uroot -p processlist 查看到大量如下信息:

Sending data select * from `rep_corp_vehicle_online_count` where corp_id = 48 and vehicle_id = 10017543

根據以上的可能是表rep_corp_vehicle_online_count的問題 做出如下測試:

查看表結構:

mysql> desc rep_corp_vehicle_online_count;
+-------------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------------+-------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| corp_id | int(11) | NO | | NULL | |
| vehicle_id | int(11) | NO | | NULL | |
| online_day | varchar(20) | NO | | NULL | |
| loc_total | int(11) | NO | | NULL | |
| create_time | datetime | NO | | NULL | |
| update_time | datetime | NO | | NULL | |
+-------------+-------------+------+-----+---------+----------------+
7 rows in set (0.00 sec) 

查看索引,只有主鍵索引:

mysql> show index from rep_corp_vehicle_online_count;
+-------------------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------------------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| rep_corp_vehicle_online_count | 0 | PRIMARY | 1 | id | A | 1247259 | NULL | NULL | | BTREE | | |
+-------------------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
1 row in set (0.00 sec) 

代碼執行情況:

mysql>explain select * from rep_corp_vehicle_online_count where corp_id = 79 and vehicle_id = 10016911 and online_day = '2016-03-29'\G
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: rep_corp_vehicle_online_count
type: ALL
possible_keys: NULL
key: NULL
key_len: NULL
ref: NULL
rows: 1248495
Extra: Using where
1 row in set (0.00 sec) 

表數據分析情況,重復數據很多:

mysql> select count(distinct corp_id) from rep_corp_vehicle_online_count;
+-------------------------+
| count(distinct corp_id) |
+-------------------------+
| 18 |
+-------------------------+
1 row in set (0.63 sec)
mysql> select count(corp_id) from rep_corp_vehicle_online_count; 
+----------------+
| count(corp_id) |
+----------------+
| 1239573 |
+----------------+
1 row in set (0.00 sec)
mysql> select count(distinct vehicle_id) from rep_corp_vehicle_online_count; 
+----------------------------+
| count(distinct vehicle_id) |
+----------------------------+
| 2580 |
+----------------------------+
1 row in set (1.03 sec)
mysql>explain select count(vehicle_id) from rep_corp_vehicle_online_count; 
+-------------------+
| count(vehicle_id) |
+-------------------+
| 1239911 |
+-------------------+
1 row in set (0.00 sec) 

最後處理,創建索引:

mysql> create index r_c_v on rep_corp_vehicle_online_count(corp_id,vehicle_id); 
Query OK, 1487993 rows affected (6.09 sec)
Records: 1487993 Duplicates: 0 Warnings: 0
mysql> show index from rep_corp_vehicle_online_count;
+-------------------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------------------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| rep_corp_vehicle_online_count | 0 | PRIMARY | 1 | id | A | 1490176 | NULL | NULL | | BTREE | | |
| rep_corp_vehicle_online_count | 1 | r_c_v | 1 | corp_id | A | 18 | NULL | NULL | | BTREE | | |
| rep_corp_vehicle_online_count | 1 | r_c_v | 2 | vehicle_id | A | 2596 | NULL | NULL | | BTREE | | |
+-------------------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
3 rows in set (0.00 sec)

添加索引過後負載降低到了1.73:

以上內容是小編給大家介紹的Mysql數據庫之索引優化 ,希望對大家學習有所幫助!

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