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 |>| TABLE | a | t3 |>| TABLE | a | t3 | NULL | 0 | 0 | 0 |+-------------+---------------+-------------+-------------+------------+------------+-------------+3 rows in set (0.01 sec) mysql> explain select>ERROR 1046 (3D000): No database selectedmysql> explain select>+----+-------------+-------+------+---------------+--------+---------+-------+------+-------------+|>+----+-------------+-------+------+---------------+--------+---------+-------+------+-------------+|1 | SIMPLE | t3 | ref|>+----+-------------+-------+------+---------------+--------+---------+-------+------+-------------+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 |>| TABLE | a | t3 |>| 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 namesYou can turn off this feature to get a quicker startup with -A Database changedmysql> select>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 |>| TABLE | a | t3 |>| TABLE | a | t3 | NULL | 0 | 0 | 0 |+-------------+---------------+-------------+-------------+------------+------------+-------------+3 rows in set (0.00 sec) mysql> select>|>+------+| 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 |>| TABLE | a | t3 |>| 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 |>| TABLE | a | t3 |>| 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 |>| TABLE | a | t3 |>| 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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