There are two issues you need to look at

ISSUE #1 : Characters Vs Bytes

Since UTF-8 uses 3 bytes per characters, you may not have allocated enough for character fields.

ISSUE #2 : InnoDB Row Length

By default, an index key for a single-column index can be up to 767 bytes. The same length limit applies to any index key prefix. See Section 13.1.13, “CREATE INDEX Syntax”. For example, you might hit this limit with a column prefix index of more than 255 characters on a TEXT or VARCHAR column, assuming a UTF-8 character set and the maximum of 3 bytes for each character. When the innodb_large_prefix configuration option is enabled, this length limit is raised to 3072 bytes, for InnoDB tables that use the DYNAMIC and COMPRESSED row formats.

When you attempt to specify an index prefix length longer than allowed, the length is silently reduced to the maximum length. This configuration option changes the error handling for some combinations of row format and prefix length longer than the maximum allowed. See innodb_large_prefix for details.

The InnoDB internal maximum key length is 3500 bytes, but MySQL itself restricts this to 3072 bytes. This limit applies to the length of the combined index key in a multi-column index.

The maximum row length, except for variable-length columns (VARBINARY, VARCHAR, BLOB and TEXT), is slightly less than half of a database page. That is, the maximum row length is about 8000 bytes. LONGBLOB and LONGTEXT columns must be less than 4GB, and the total row length, including BLOB and TEXT columns, must be less than 4GB.

If a row is less than half a page long, all of it is stored locally within the page. If it exceeds half a page, variable-length columns are chosen for external off-page storage until the row fits within half a page, as described in Section 14.3.12.2, “File Space Management”.

Although InnoDB supports row sizes larger than 65,535 bytes internally, MySQL itself imposes a row-size limit of 65,535 for the combined size of all columns:

mysql> CREATE TABLE t (a VARCHAR(8000), b VARCHAR(10000), -> c VARCHAR(10000), d VARCHAR(10000), e VARCHAR(10000), -> f VARCHAR(10000), g VARCHAR(10000)) ENGINE=InnoDB; ERROR 1118 (42000): Row size too large. The maximum row size for the used table type, not counting BLOBs, is 65535. You have to change some columns to TEXT or BLOBs See Section E.10.4, “Table Column-Count and Row-Size Limits”.

I have some rather distressing news: ORDER BY can still wreak some havoc with filesorts.

With all the hype about this being addressed and fixed, there is simply no way to get InnoDB to effectively use the index on an ORDER BY.

Start with the Ground Zero of InnoDB row data, the Clustered Index.

Rows are tagged with

• a 6-byte transaction ID field
• a 7-byte roll pointer field

Rows tend to be ordered by the whatever order the data was entered. The columns of a PRIMARY KEY are included in secondary indexes and are used to search for rows in the Clustered Index, Unfortunately, the two ID fields are not really used in dictating any ordering of rows within the Clustered Index. (For more info, please see MySQL Documentation on InnoDB Physical Row Structure)

Here is something even more disturbing: Did you know you could order rows in a table by the columns of the PRIMARY KEY or any arbitrary ordering you choose?

Here is the syntax:

ALTER TABLE tblname ORDER BY col_name [, col_name] ...

This could speed up some queries that a PRIMARY KEY ordered, but what's disturbing is that it only applies to MyISAM tables. Why not InnoDB ?

According to the MySQL Documentation on ALTER TABLE ... ORDER BY:

ORDER BY enables you to create the new table with the rows in a specific order. Note that the table does not remain in this order after inserts and deletes. This option is useful primarily when you know that you are mostly to query the rows in a certain order most of the time. By using this option after major changes to the table, you might be able to get higher performance. In some cases, it might make sorting easier for MySQL if the table is in order by the column that you want to order it by later.

ORDER BY syntax permits one or more column names to be specified for sorting, each of which optionally can be followed by ASC or DESC to indicate ascending or descending sort order, respectively. The default is ascending order. Only column names are permitted as sort criteria; arbitrary expressions are not permitted. This clause should be given last after any other clauses.

ORDER BY does not make sense for InnoDB tables because InnoDB always orders table rows according to the clustered index.

This comes as no surprise to me since I mentioned this in one of my earlier posts : (Aug 29, 2011 : Preordering the table by a specified column)

Therefore, doing an ORDER BY on an InnoDB table never guarantees proper index selection due to its internal index organization. Thus, one should not be surprised by a filesort on an InnoDB table no matter what secondary indexes the table has.