MySQL分析表结果奇怪的行为

Question

我注意到运行时得到的表总计：

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

导致总数不正确。 我还读到这样做：

analyze table 'my_table';

将正确更新信息。 但似乎并非如此。 因此，要设置基准：

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

接下来，统计数据显示：

  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)

显然，那是不对的，所以我进行分析并再次检查：

  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，它改变了，但是仍然是错误的。 所以我做了几次：

  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)

如您所见，我从来没有得到相同的数字，而且它们都不是实际的行数。 我的问题是：这是否表明我的数据库有问题（在所有表上都存在问题），或者这仅仅是MySQL中的错误？

我的环境的详细信息：

服务器版本：5.6.43 MySQL Community Server（GPL）所有表均为INNODB，字符集为utf8

Answer 1

对于InnoDB， table_rows统计信息是估计值 ，而不是精确的计数。 该值不能保证是确切的行数。

不，这不是MySQL中的错误。 InnoDB统计信息没有错。 行为记录在《 MySQL参考手册》中。

参考文献：

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