MySQL分析表結果奇怪的行為

Question

我注意到運行時得到的表總計：

SELECT TABLE_NAME, TABLE_ROWS FROM `information_schema`.`tables` WHERE `table_schema` = 'my_database';

導致總數不正確。 我還讀到這樣做：

analyze table 'my_table';

將正確更新信息。 但似乎並非如此。 因此，要設置基准：

  mysql> select count(*) from my_table;
  +----------+
  | count(*) |
  +----------+
  |    61782 |
  +----------+
  1 row in set (0.01 sec)

接下來，統計數據顯示：

  mysql> SELECT TABLE_NAME, TABLE_ROWS FROM `information_schema`.`tables` WHERE `table_schema` = 'my_database' AND TABLE_NAME = 'my_table';
  +--------------------+------------+
  | TABLE_NAME         | TABLE_ROWS |
  +--------------------+------------+
  | my_table           |      58378 |
  +--------------------+------------+
  1 row in set (0.00 sec)

顯然，那是不對的，所以我進行分析並再次檢查：

  mysql> analyze table my_table;
  +------------------------------+---------+----------+----------+
  | Table                        | Op      | Msg_type | Msg_text |
  +------------------------------+---------+----------+----------+
  | my_database.my_table         | analyze | status   | OK       |
  +------------------------------+---------+----------+----------+
  1 row in set (0.02 sec)

  mysql> SELECT TABLE_NAME, TABLE_ROWS FROM `information_schema`.`tables` WHERE `table_schema` = 'my_database' AND TABLE_NAME = 'my_table';
  +--------------------+------------+
  | TABLE_NAME         | TABLE_ROWS |
  +--------------------+------------+
  | my_table           |      56439 |
  +--------------------+------------+
  1 row in set (0.00 sec)

好的，它改變了，但是仍然是錯誤的。 所以我做了幾次：

  mysql> analyze table my_table;
  +------------------------------+---------+----------+----------+
  | Table                        | Op      | Msg_type | Msg_text |
  +------------------------------+---------+----------+----------+
  | my_database.my_table         | analyze | status   | OK       |
  +------------------------------+---------+----------+----------+
  1 row in set (0.02 sec)

  mysql> SELECT TABLE_NAME, TABLE_ROWS FROM `information_schema`.`tables` WHERE `table_schema` = 'my_database' AND TABLE_NAME = 'my_table';
  +--------------------+------------+
  | TABLE_NAME         | TABLE_ROWS |
  +--------------------+------------+
  | my_table           |      58766 |
  +--------------------+------------+
  1 row in set (0.00 sec)

  mysql> analyze table my_table;
  +------------------------------+---------+----------+----------+
  | Table                        | Op      | Msg_type | Msg_text |
  +------------------------------+---------+----------+----------+
  | my_database.my_table         | analyze | status   | OK       |
  +------------------------------+---------+----------+----------+
  1 row in set (0.02 sec)

  mysql> SELECT TABLE_NAME, TABLE_ROWS FROM `information_schema`.`tables` WHERE `table_schema` = 'my_database' AND TABLE_NAME = 'my_table';
  +--------------------+------------+
  | TABLE_NAME         | TABLE_ROWS |
  +--------------------+------------+
  | my_table           |      65749 |
  +--------------------+------------+
  1 row in set (0.00 sec)

  mysql> analyze table my_table;
  +------------------------------+---------+----------+----------+
  | Table                        | Op      | Msg_type | Msg_text |
  +------------------------------+---------+----------+----------+
  | my_database.my_table         | analyze | status   | OK       |
  +------------------------------+---------+----------+----------+
  1 row in set (0.02 sec)

  mysql> SELECT TABLE_NAME, TABLE_ROWS FROM `information_schema`.`tables` WHERE `table_schema` = 'my_database' AND TABLE_NAME = 'my_table';
  +--------------------+------------+
  | TABLE_NAME         | TABLE_ROWS |
  +--------------------+------------+
  | my_table           |      61870 |
  +--------------------+------------+
  1 row in set (0.00 sec)

如您所見，我從來沒有得到相同的數字，而且它們都不是實際的行數。 我的問題是：這是否表明我的數據庫有問題（在所有表上都存在問題），或者這僅僅是MySQL中的錯誤？

我的環境的詳細信息：

服務器版本：5.6.43 MySQL Community Server（GPL）所有表均為INNODB，字符集為utf8

Answer 1

對於InnoDB， table_rows統計信息是估計值 ，而不是精確的計數。 該值不能保證是確切的行數。

不，這不是MySQL中的錯誤。 InnoDB統計信息沒有錯。 行為記錄在《 MySQL參考手冊》中。

參考文獻：

https://dev.mysql.com/doc/refman/5.6/zh-CN/index-statistics.html

https://dev.mysql.com/doc/refman/5.6/zh-CN/innodb-persistent-stats.html