The attribute KEY_BLOCK_SIZE is permitted only when ROW_FORMAT is specified as COMPRESSED or is omitted. Specifying a KEY_BLOCK_SIZE with any other ROW_FORMAT generates a warning that you can view with SHOW WARNINGS. However, the table is non-compressed; the specified KEY_BLOCK_SIZE is ignored).

If you are running in InnoDB strict mode, the combination of a KEY_BLOCK_SIZE with any ROW_FORMAT other than COMPRESSED generates an error, not a warning, and the table is not created.

Table 3.1, “Meaning of CREATE TABLE and ALTER TABLE options” summarizes how the various options on CREATE TABLE and ALTER TABLE are handled.

Table 3.2, “CREATE/ALTER TABLE Warnings and Errors when InnoDB Strict Mode is OFF” summarizes error conditions that occur with certain combinations of configuration parameters and options on the CREATE TABLE or ALTER TABLE commands, and how the options appear in the output of SHOW TABLE STATUS.

When InnoDB strict mode is OFF, InnoDB creates or alters the table, but may ignore certain settings, as shown below. You can see the warning messages in the MySQL error log. When InnoDB strict mode is ON, these specified combinations of options generate errors, and the table is not created or altered. You can see the full description of the error condition with SHOW ERRORS. For example:

mysql> CREATE TABLE x (id INT PRIMARY KEY, c INT)

-> ENGINE=INNODB KEY_BLOCK_SIZE=33333;

ERROR 1005 (HY000): Can't create table 'test.x' (errno: 1478)

mysql> SHOW ERRORS;
+-------+------+-------------------------------------------+ 
| Level | Code | Message                                   | 
+-------+------+-------------------------------------------+ 
| Error | 1478 | InnoDB: invalid KEY_BLOCK_SIZE=33333.     | 
| Error | 1005 | Can't create table 'test.x' (errno: 1478) | 
+-------+------+-------------------------------------------+ 

2 rows in set (0.00 sec)

When InnoDB strict mode is ON (innodb_strict_mode=1), the InnoDB storage engine rejects invalid ROW_FORMAT or KEY_BLOCK_SIZE parameters. For compatibility with the built-in InnoDB in MySQL, InnoDB strict mode is not enabled by default, and in this default non-strict mode, the InnoDB storage engine issues warnings (not errors) for ignored invalid parameters.

Note that it is not possible to see the chosen KEY_BLOCK_SIZE using SHOW TABLE STATUS. The command SHOW CREATE TABLE displays the KEY_BLOCK_SIZE (even if it was ignored by InnoDB). The real compressed page size inside InnoDB cannot be displayed by MySQL.