mysql中查看索引是否被使用到

http://blog.sina.com.cn/s/blog_5037eacb0102vm5c.html

官方MySQL中查看索引是否被使用到：

 

在percona版本或marida中可以通过 information_schea.index_statistics查看得到，

在官方版本中如何查看呢？

 

 

select object_type,object_schema,object_name,index_name,count_star,count_read,COUNT_FETCH from performance_schema.table_io_waits_summary_by_index_usage;

应该可以通过上面的sql得到。 如果read,fetch的次数都为0的话，应该是没有被使用过的。

 

通过下面的例子，可以证实：

 

启动mysql:

mysql> show create table a.t3;

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

| Table | Create Table                                                                                                                                                                         |

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

| t3    | CREATE TABLE `t3` (

  `id` int(11) DEFAULT NULL,

  `name` varchar(10) NOT NULL DEFAULT 'bb',

  KEY `idx_t3` (`id`),

  KEY `idx_t3_name` (`name`)

) ENGINE=InnoDB DEFAULT CHARSET=utf8 |

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

1 row in set (0.01 sec)

 

mysql> select object_type,object_schema,object_name,index_name,count_star,count_read,COUNT_FETCH from performance_schema.table_io_waits_summary_by_index_usage where object_name='t3';

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

| object_type | object_schema | object_name | index_name  | count_star | count_read | COUNT_FETCH |

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

| TABLE       | a             | t3          | idx_t3      |          0 |          0 |           0 |

| TABLE       | a             | t3          | idx_t3_name |          0 |          0 |           0 |

| TABLE       | a             | t3          | NULL        |          0 |          0 |           0 |

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

3 rows in set (0.01 sec)

 

mysql> explain select id from t3 where id=1;

ERROR 1046 (3D000): No database selected

mysql> explain select id from a.t3 where id=1;

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

| id | select_type | table | type | possible_keys | key    | key_len | ref   | rows | Extra       |

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

|  1 | SIMPLE      | t3    | ref  | idx_t3        | idx_t3 | 5       | const |    1 | Using index |

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

1 row in set (0.00 sec)

 

mysql> select object_type,object_schema,object_name,index_name,count_star,count_read,COUNT_FETCH from performance_schema.table_io_waits_summary_by_index_usage where object_name='t3';

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

| object_type | object_schema | object_name | index_name  | count_star | count_read | COUNT_FETCH |

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

| TABLE       | a             | t3          | idx_t3      |          0 |          0 |           0 |

| TABLE       | a             | t3          | idx_t3_name |          0 |          0 |           0 |

| TABLE       | a             | t3          | NULL        |          0 |          0 |           0 |

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

3 rows in set (0.01 sec)

 

mysql> use a;

Reading table information for completion of table and column names

You can turn off this feature to get a quicker startup with -A

 

Database changed

mysql> select id from t3 where id=1;

Empty set (0.00 sec)

 

mysql> select object_type,object_schema,object_name,index_name,count_star,count_read,COUNT_FETCH from performance_schema.table_io_waits_summary_by_index_usage where object_name='t3';

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

| object_type | object_schema | object_name | index_name  | count_star | count_read | COUNT_FETCH |

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

| TABLE       | a             | t3          | idx_t3      |          1 |          1 |           1 |

| TABLE       | a             | t3          | idx_t3_name |          0 |          0 |           0 |

| TABLE       | a             | t3          | NULL        |          0 |          0 |           0 |

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

3 rows in set (0.00 sec)

 

mysql> select id from t3 where id=10;                                                                                               +------+

| id   |

+------+

|   10 |

|   10 |

+------+

2 rows in set (0.00 sec)

 

mysql> select object_type,object_schema,object_name,index_name,count_star,count_read,COUNT_FETCH from performance_schema.table_io_waits_summary_by_index_usage where object_name='t3';

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

| object_type | object_schema | object_name | index_name  | count_star | count_read | COUNT_FETCH |

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

| TABLE       | a             | t3          | idx_t3      |          4 |          4 |           4 |

| TABLE       | a             | t3          | idx_t3_name |          0 |          0 |           0 |

| TABLE       | a             | t3          | NULL        |          0 |          0 |           0 |

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

3 rows in set (0.01 sec)

 

mysql> select name from t3 where name='a';

Empty set (0.00 sec)

 

mysql> select object_type,object_schema,object_name,index_name,count_star,count_read,COUNT_FETCH from performance_schema.table_io_waits_summary_by_index_usage where object_name='t3';

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

| object_type | object_schema | object_name | index_name  | count_star | count_read | COUNT_FETCH |

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

| TABLE       | a             | t3          | idx_t3      |          4 |          4 |           4 |

| TABLE       | a             | t3          | idx_t3_name |          1 |          1 |           1 |

| TABLE       | a             | t3          | NULL        |          0 |          0 |           0 |

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

3 rows in set (0.01 sec)

 

mysql> select name from t3 where name='name1';

+-------+

| name  |

+-------+

| name1 |

+-------+

1 row in set (0.01 sec)

 

mysql> select object_type,object_schema,object_name,index_name,count_star,count_read,COUNT_FETCH from performance_schema.table_io_waits_summary_by_index_usage where object_name='t3';

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

| object_type | object_schema | object_name | index_name  | count_star | count_read | COUNT_FETCH |

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

| TABLE       | a             | t3          | idx_t3      |          4 |          4 |           4 |

| TABLE       | a             | t3          | idx_t3_name |          3 |          3 |           3 |

| TABLE       | a             | t3          | NULL        |          0 |          0 |           0 |

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

3 rows in set (0.01 sec)

 

索引被使用之后， 对应的值会增加。