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打开userstat参数，然后让MySQL运行一段时间。
之后可以在INFORMATION_SCHEMA.INDEX_STATISTICS表中查询到索引的使用频率。

mysql> show global variables like '%users%';

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

| Variable_name | Value |

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

| userstat | OFF |

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

1 row in set (0.00 sec)

mysql> select * from information_schema.index_statistics;

Empty set (0.00 sec)

mysql> set global userstat=1;

Query OK, 0 rows affected (0.00 sec)

mysql> show global variables like '%users%';

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

| Variable_name | Value |

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

| userstat | ON |

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

1 row in set (0.00 sec)

mysql> select * from information_schema.index_statistics;

Empty set (0.00 sec)

mysql> explain select * from emp where hiredate > '1982-01-01' and deptno = 20;

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

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

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

| 1 | SIMPLE | emp | range | idx_date_sal_job,idx_date | idx_date_sal_job | 4 | NULL | 3 | Using where |

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

1 row in set (0.00 sec)

mysql> select * from information_schema.index_statistics;

Empty set (0.00 sec)

mysql> select * from emp where hiredate > '1982-01-01' and deptno = 20;

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

| empno | ename | job | mgr | hiredate | sal | comm | deptno |

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

| 7788 | SCOTT | ANALYST | 7566 | 1982-12-09 00:00:00 | 3000 | NULL | 20 |

| 7876 | ADAMS | CLERK | 7788 | 1983-01-12 00:00:00 | 1100 | NULL | 20 |

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

2 rows in set (0.00 sec)

mysql> select * from information_schema.index_statistics;

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

| TABLE_SCHEMA | TABLE_NAME | INDEX_NAME | ROWS_READ |

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

| test | emp | idx_date_sal_job | 3 |

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

1 row in set (0.04 sec)

mysql> select * from emp;

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

| empno | ename | job | mgr | hiredate | sal | comm | deptno |

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

| 7369 | SMITH | CLERK | 7902 | 1980-12-17 00:00:00 | 800 | NULL | 20 |

| 7499 | ALLEN | SALESMAN | 7698 | 1981-02-20 00:00:00 | 1600 | 300 | 30 |

| 7521 | WARD | SALESMAN | 7698 | 1981-02-22 00:00:00 | 1250 | 500 | 30 |

| 7566 | JONES | MANAGER | 7839 | 1981-04-02 00:00:00 | 2975 | NULL | 20 |

| 7654 | MARTIN | SALESMAN | 7698 | 1981-09-28 00:00:00 | 1250 | 1400 | 30 |

| 7698 | BLAKE | MANAGER | 7839 | 1981-05-01 00:00:00 | 2850 | NULL | 30 |

| 7782 | CLARK | MANAGER | 7839 | 1981-06-09 00:00:00 | 2450 | NULL | 10 |

| 7788 | SCOTT | ANALYST | 7566 | 1982-12-09 00:00:00 | 3000 | NULL | 20 |

| 7839 | KING | PRESIDENT | NULL | 1981-11-17 00:00:00 | 5000 | NULL | 10 |

| 7844 | TURNER | SALESMAN | 7698 | 1981-09-08 00:00:00 | 1500 | 0 | 30 |

| 7876 | ADAMS | CLERK | 7788 | 1983-01-12 00:00:00 | 1100 | NULL | 20 |

| 7900 | JAMES | CLERK | 7698 | 1981-12-03 00:00:00 | 950 | NULL | 30 |

| 7902 | FORD | ANALYST | 7566 | 1981-12-03 00:00:00 | 3000 | NULL | 20 |

| 7934 | MILLER | CLERK | 7782 | 1982-01-23 00:00:00 | 1300 | NULL | 10 |

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

14 rows in set (0.00 sec)

mysql> select * from information_schema.index_statistics;

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

| TABLE_SCHEMA | TABLE_NAME | INDEX_NAME | ROWS_READ |

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

| test | emp | PRIMARY | 14 |

| test | emp | idx_date_sal_job | 3 |

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

2 rows in set (0.00 sec)

mysql> select * from emp where hiredate > '1982-01-01' and deptno = 20;

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

| empno | ename | job | mgr | hiredate | sal | comm | deptno |

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

| 7788 | SCOTT | ANALYST | 7566 | 1982-12-09 00:00:00 | 3000 | NULL | 20 |

| 7876 | ADAMS | CLERK | 7788 | 1983-01-12 00:00:00 | 1100 | NULL | 20 |

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

2 rows in set (0.00 sec)

mysql> select * from emp;

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

| empno | ename | job | mgr | hiredate | sal | comm | deptno |

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

| 7369 | SMITH | CLERK | 7902 | 1980-12-17 00:00:00 | 800 | NULL | 20 |

| 7499 | ALLEN | SALESMAN | 7698 | 1981-02-20 00:00:00 | 1600 | 300 | 30 |

| 7521 | WARD | SALESMAN | 7698 | 1981-02-22 00:00:00 | 1250 | 500 | 30 |

| 7566 | JONES | MANAGER | 7839 | 1981-04-02 00:00:00 | 2975 | NULL | 20 |

| 7654 | MARTIN | SALESMAN | 7698 | 1981-09-28 00:00:00 | 1250 | 1400 | 30 |

| 7698 | BLAKE | MANAGER | 7839 | 1981-05-01 00:00:00 | 2850 | NULL | 30 |

| 7782 | CLARK | MANAGER | 7839 | 1981-06-09 00:00:00 | 2450 | NULL | 10 |

| 7788 | SCOTT | ANALYST | 7566 | 1982-12-09 00:00:00 | 3000 | NULL | 20 |

| 7839 | KING | PRESIDENT | NULL | 1981-11-17 00:00:00 | 5000 | NULL | 10 |

| 7844 | TURNER | SALESMAN | 7698 | 1981-09-08 00:00:00 | 1500 | 0 | 30 |

| 7876 | ADAMS | CLERK | 7788 | 1983-01-12 00:00:00 | 1100 | NULL | 20 |

| 7900 | JAMES | CLERK | 7698 | 1981-12-03 00:00:00 | 950 | NULL | 30 |

| 7902 | FORD | ANALYST | 7566 | 1981-12-03 00:00:00 | 3000 | NULL | 20 |

| 7934 | MILLER | CLERK | 7782 | 1982-01-23 00:00:00 | 1300 | NULL | 10 |

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

14 rows in set (0.00 sec)

mysql> select * from information_schema.index_statistics;

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

| TABLE_SCHEMA | TABLE_NAME | INDEX_NAME | ROWS_READ |

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

| test | emp | PRIMARY | 28 |

| test | emp | idx_date_sal_job | 6 |

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

2 rows in set (0.00 sec)

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