Percona5.5如何定位未使用的索引

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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。

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

2. +---------------+-------+

3. | Variable_name | Value |

4. +---------------+-------+

5. | userstat | OFF |

6. +---------------+-------+

7. 1 row in set (0.00 sec)

9. mysql> select * from information_schema.index_statistics;

10. Empty set (0.00 sec)

12. mysql> set global userstat=1;

13. Query OK, 0 rows affected (0.00 sec)

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

16. +---------------+-------+

17. | Variable_name | Value |

18. +---------------+-------+

19. | userstat | ON |

20. +---------------+-------+

21. 1 row in set (0.00 sec)

23. mysql> select * from information_schema.index_statistics;

24. Empty set (0.00 sec)

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

27. +----+-------------+-------+-------+---------------------------+------------------+---------+------+------+-------------+

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

29. +----+-------------+-------+-------+---------------------------+------------------+---------+------+------+-------------+

30. | 1 | SIMPLE | emp | range | idx_date_sal_job,idx_date | idx_date_sal_job | 4 | NULL | 3 | Using where |

31. +----+-------------+-------+-------+---------------------------+------------------+---------+------+------+-------------+

32. 1 row in set (0.00 sec)

34. mysql> select * from information_schema.index_statistics;

35. Empty set (0.00 sec)

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

38. +-------+-------+---------+------+---------------------+------+------+--------+

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

40. +-------+-------+---------+------+---------------------+------+------+--------+

41. | 7788 | SCOTT | ANALYST | 7566 | 1982-12-09 00:00:00 | 3000 | NULL | 20 |

42. | 7876 | ADAMS | CLERK | 7788 | 1983-01-12 00:00:00 | 1100 | NULL | 20 |

43. +-------+-------+---------+------+---------------------+------+------+--------+

44. 2 rows in set (0.00 sec)

46. mysql> select * from information_schema.index_statistics;

47. +--------------+------------+------------------+-----------+

48. | TABLE_SCHEMA | TABLE_NAME | INDEX_NAME | ROWS_READ |

49. +--------------+------------+------------------+-----------+

50. | test | emp | idx_date_sal_job | 3 |

51. +--------------+------------+------------------+-----------+

52. 1 row in set (0.04 sec)

54. mysql> select * from emp;

55. +-------+--------+-----------+------+---------------------+------+------+--------+

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

57. +-------+--------+-----------+------+---------------------+------+------+--------+

58. | 7369 | SMITH | CLERK | 7902 | 1980-12-17 00:00:00 | 800 | NULL | 20 |

59. | 7499 | ALLEN | SALESMAN | 7698 | 1981-02-20 00:00:00 | 1600 | 300 | 30 |

60. | 7521 | WARD | SALESMAN | 7698 | 1981-02-22 00:00:00 | 1250 | 500 | 30 |

61. | 7566 | JONES | MANAGER | 7839 | 1981-04-02 00:00:00 | 2975 | NULL | 20 |

62. | 7654 | MARTIN | SALESMAN | 7698 | 1981-09-28 00:00:00 | 1250 | 1400 | 30 |

63. | 7698 | BLAKE | MANAGER | 7839 | 1981-05-01 00:00:00 | 2850 | NULL | 30 |

64. | 7782 | CLARK | MANAGER | 7839 | 1981-06-09 00:00:00 | 2450 | NULL | 10 |

65. | 7788 | SCOTT | ANALYST | 7566 | 1982-12-09 00:00:00 | 3000 | NULL | 20 |

66. | 7839 | KING | PRESIDENT | NULL | 1981-11-17 00:00:00 | 5000 | NULL | 10 |

67. | 7844 | TURNER | SALESMAN | 7698 | 1981-09-08 00:00:00 | 1500 | 0 | 30 |

68. | 7876 | ADAMS | CLERK | 7788 | 1983-01-12 00:00:00 | 1100 | NULL | 20 |

69. | 7900 | JAMES | CLERK | 7698 | 1981-12-03 00:00:00 | 950 | NULL | 30 |

70. | 7902 | FORD | ANALYST | 7566 | 1981-12-03 00:00:00 | 3000 | NULL | 20 |

71. | 7934 | MILLER | CLERK | 7782 | 1982-01-23 00:00:00 | 1300 | NULL | 10 |

72. +-------+--------+-----------+------+---------------------+------+------+--------+

73. 14 rows in set (0.00 sec)

75. mysql> select * from information_schema.index_statistics;

76. +--------------+------------+------------------+-----------+

77. | TABLE_SCHEMA | TABLE_NAME | INDEX_NAME | ROWS_READ |

78. +--------------+------------+------------------+-----------+

79. | test | emp | PRIMARY | 14 |

80. | test | emp | idx_date_sal_job | 3 |

81. +--------------+------------+------------------+-----------+

82. 2 rows in set (0.00 sec)

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

85. +-------+-------+---------+------+---------------------+------+------+--------+

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

87. +-------+-------+---------+------+---------------------+------+------+--------+

88. | 7788 | SCOTT | ANALYST | 7566 | 1982-12-09 00:00:00 | 3000 | NULL | 20 |

89. | 7876 | ADAMS | CLERK | 7788 | 1983-01-12 00:00:00 | 1100 | NULL | 20 |

90. +-------+-------+---------+------+---------------------+------+------+--------+

91. 2 rows in set (0.00 sec)

93. mysql> select * from emp;

94. +-------+--------+-----------+------+---------------------+------+------+--------+

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

96. +-------+--------+-----------+------+---------------------+------+------+--------+

97. | 7369 | SMITH | CLERK | 7902 | 1980-12-17 00:00:00 | 800 | NULL | 20 |

98. | 7499 | ALLEN | SALESMAN | 7698 | 1981-02-20 00:00:00 | 1600 | 300 | 30 |

99. | 7521 | WARD | SALESMAN | 7698 | 1981-02-22 00:00:00 | 1250 | 500 | 30 |

100. | 7566 | JONES | MANAGER | 7839 | 1981-04-02 00:00:00 | 2975 | NULL | 20 |

101. | 7654 | MARTIN | SALESMAN | 7698 | 1981-09-28 00:00:00 | 1250 | 1400 | 30 |

102. | 7698 | BLAKE | MANAGER | 7839 | 1981-05-01 00:00:00 | 2850 | NULL | 30 |

103. | 7782 | CLARK | MANAGER | 7839 | 1981-06-09 00:00:00 | 2450 | NULL | 10 |

104. | 7788 | SCOTT | ANALYST | 7566 | 1982-12-09 00:00:00 | 3000 | NULL | 20 |

105. | 7839 | KING | PRESIDENT | NULL | 1981-11-17 00:00:00 | 5000 | NULL | 10 |

106. | 7844 | TURNER | SALESMAN | 7698 | 1981-09-08 00:00:00 | 1500 | 0 | 30 |

107. | 7876 | ADAMS | CLERK | 7788 | 1983-01-12 00:00:00 | 1100 | NULL | 20 |

108. | 7900 | JAMES | CLERK | 7698 | 1981-12-03 00:00:00 | 950 | NULL | 30 |

109. | 7902 | FORD | ANALYST | 7566 | 1981-12-03 00:00:00 | 3000 | NULL | 20 |

110. | 7934 | MILLER | CLERK | 7782 | 1982-01-23 00:00:00 | 1300 | NULL | 10 |

111. +-------+--------+-----------+------+---------------------+------+------+--------+

112. 14 rows in set (0.00 sec)

114. mysql> select * from information_schema.index_statistics;

115. +--------------+------------+------------------+-----------+

116. | TABLE_SCHEMA | TABLE_NAME | INDEX_NAME | ROWS_READ |

117. +--------------+------------+------------------+-----------+

118. | test | emp | PRIMARY | 28 |

119. | test | emp | idx_date_sal_job | 6 |

120. +--------------+------------+------------------+-----------+

121. 2 rows in set (0.00 sec)

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