mysql的优化措施，从sql优化做起

show status like ‘Handler_read%‘;

如果Handler_read_rnd_next的值比较高，说明索引不正确或者查询没有使用到索引

有索引:


mysql> select * from dd;
+----+
| a  |
+----+
|  1 |
|  2 |
|  3 |
|  4 |
|  5 |
|  6 |
|  7 |
|  8 |
|  9 |
| 10 |
| 11 |
| 12 |
| 13 |
+----+
13 rows in set (0.00 sec)

mysql> show create table dd;
+-------+----------------------------------------
| Table | Create Table
+-------+----------------------------------------
| dd    | CREATE TABLE `dd` (
  `a` int(11) NOT NULL,
  PRIMARY KEY (`a`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------+----------------------------------------
1 row in set (0.02 sec)

mysql> select * from dd where a=10;
+----+
| a  |
+----+
| 10 |
+----+
1 row in set (0.00 sec)

mysql> show status like ‘Handler_read%‘;
+-----------------------+-------+
| Variable_name         | Value |
+-----------------------+-------+
| Handler_read_first    | 0     |
| Handler_read_key      | 1     |    //增加的是这个值
| Handler_read_last     | 0     |
| Handler_read_next     | 0     |
| Handler_read_prev     | 0     |
| Handler_read_rnd      | 0     |
| Handler_read_rnd_next | 2     |
+-----------------------+-------+
7 rows in set (0.00 sec)

无索引:




mysql> show create table q;
+-------+------------------------------------------------------------------------------------+
| Table | Create Table                                                                       |
+-------+------------------------------------------------------------------------------------+
| q     | CREATE TABLE `q` (
  `a` int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------+------------------------------------------------------------------------------------+
1 row in set (0.00 sec)


mysql> select * from q where a=10;
+------+
| a    |
+------+
|   10 |
+------+
1 row in set (0.00 sec)

mysql> show status like ‘Handler_read%‘;
+-----------------------+-------+
| Variable_name         | Value |
+-----------------------+-------+
| Handler_read_first    | 1     |
| Handler_read_key      | 1     |
| Handler_read_last     | 0     |
| Handler_read_next     | 0     |
| Handler_read_prev     | 0     |
| Handler_read_rnd      | 0     |
| Handler_read_rnd_next | 56    |
+-----------------------+-------+
7 rows in set (0.00 sec)

mysql> select * from q where a=11;
+------+
| a    |
+------+
|   11 |
+------+
1 row in set (0.00 sec)

mysql> show status like ‘Handler_read%‘;
+-----------------------+-------+
| Variable_name         | Value |
+-----------------------+-------+
| Handler_read_first    | 2     |
| Handler_read_key      | 2     |
| Handler_read_last     | 0     |
| Handler_read_next     | 0     |
| Handler_read_prev     | 0     |
| Handler_read_rnd      | 0     |
| Handler_read_rnd_next | 70    |
+-----------------------+-------+
7 rows in set (0.01 sec)

简单实用的优化方法

1. 定期检查表和分析表
   分析表语法：

   1	analyze table 表名；

检查表语法：

1

check table 表名；

1. 定期优化表
   • 对于字节大小不固定的字段，数据更新和删除会造成磁盘空间不释放，这时候就行优化表，可以整理磁盘碎片，提高性能
     语法如下：

     1	optimize table user(表名)；

mysql的优化措施，从sql优化做起

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