Percona 5.5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)
   

8. 
   

9. mysql> select * from information_schema.index_statistics;
   

10. Empty set (0.00 sec)
    

11. 
    

12. mysql> set global userstat=1;
    

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

14. 
    

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)
    

22. 
    

23. mysql> select * from information_schema.index_statistics;
    

24. Empty set (0.00 sec)
    

25. 
    

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)
    

33. 
    

34. mysql> select * from information_schema.index_statistics;
    

35. Empty set (0.00 sec)
    

36. 
    

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)
    

45. 
    

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)
    

53. 
    

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)
    

74. 
    

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)
    

83. 
    

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)
    

92. 
    

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)
     

113. 
     

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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