17.22 InnoDB Restrictions and Limitations

This section describes restrictions and limitations of the InnoDB storage engine.

• You cannot create a table with a column name that matches the name of an internal InnoDB column (including DB_ROW_ID, DB_TRX_ID, and DB_ROLL_PTR. This restriction applies to use of the names in any lettercase.

  mysql> CREATE TABLE t1 (c1 INT, db_row_id INT) ENGINE=INNODB;
  ERROR 1166 (42000): Incorrect column name 'db_row_id'

• SHOW TABLE STATUS does not provide accurate statistics for InnoDB tables except for the physical size reserved by the table. The row count is only a rough estimate used in SQL optimization.

• InnoDB does not keep an internal count of rows in a table because concurrent transactions might “see” different numbers of rows at the same time. Consequently, SELECT COUNT(*) statements only count rows visible to the current transaction.

  For information about how InnoDB processes SELECT COUNT(*) statements, refer to the COUNT() description in Section 14.19.1, “Aggregate Function Descriptions”.

• ROW_FORMAT=COMPRESSED is unsupported for page sizes greater than 16KB.

• A MySQL instance using a particular InnoDB page size (innodb_page_size) cannot use data files or log files from an instance that uses a different page size.

• For limitations associated with importing tables using the Transportable Tablespaces feature, see Table Import Limitations.

• For limitations associated with online DDL, see Section 17.12.8, “Online DDL Limitations”.

• For limitations associated with general tablespaces, see General Tablespace Limitations.

• For limitations associated with data-at-rest encryption, see Encryption Limitations.