官方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';

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

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

| 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;

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

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

| 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';

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

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

| 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';

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

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

| 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 |

+------+

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';

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

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

| 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';

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

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

| 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';

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

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

| 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。

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