官方mysql中檢視索引是否被使用到

psufnxk2000發表於2015-06-01
原文網址 : http://blog.itpub.net/25099483/viewspace-1680455/
MySql索引
官方mysql中檢視索引是否被使用到：

在percona版本或marida中可以通過 information_schea.index_statistics檢視得到，
在官方版本中如何檢視呢？


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;
應該可以通過上面的sql得到。 如果read,fetch的次數都為0的話，應該是沒有被使用過的。

通過下面的例子，可以證實：

啟動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)

索引被使用之後， 對應的值會增加。 


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