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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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