Percona 5.5How to locate unused indexes
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Turn on the userstat parameter and let MySQL run for a while.
You can then query the frequency of index usage in the INFORMATION_SCHEMA.INDEX_ statistics table.
Mysql > show global variables like'% users%'
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| | Variable_name | Value |
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| | 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%'
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| | Variable_name | Value |
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| | userstat | ON |
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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
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| | empno | ename | job | mgr | hiredate | sal | comm | deptno |
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| | 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
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| | TABLE_SCHEMA | TABLE_NAME | INDEX_NAME | ROWS_READ | |
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| | test | emp | idx_date_sal_job | 3 |
+-+
1 row in set (0.04 sec)
Mysql > select * from emp
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| | 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 | 1600 | 30 |
| | 7521 | WARD | SALESMAN | 7698 | 1981-02-22 00:00:00 | 1250 | 1250 | 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 | 1600 | 30 |
| | 7521 | WARD | SALESMAN | 7698 | 1981-02-22 00:00:00 | 1250 | 1250 | 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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