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。

mysql中查看索引是否被使用到

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