Index Incompatibilities

Index Incompatibilities
In MySQL 5.6.3, the length limit for index prefix keys is increased from 767 bytes to 3072 bytes, for
InnoDB tables using ROW_FORMAT=DYNAMIC or ROW_FORMAT=COMPRESSED. See Section 14.2.7,
“Limits on InnoDB Tables” for details. This change is also backported to MySQL 5.5.14. If you
downgrade from one of these releases or higher, to an earlier release with a lower length limit, the
index prefix keys could be truncated at 767 bytes or the downgrade could fail. This issue could only
occur if the configuration option innodb_large_prefix [1765] was enabled on the server being
downgraded.
If you perform a binary upgrade without dumping and reloading tables, you cannot upgrade directly
from MySQL 4.1 to 5.1 or higher. This occurs due to an incompatible change in the MyISAM table index
format in MySQL 5.0. Upgrade from MySQL 4.1 to 5.0 and repair all MyISAM tables. Then upgrade
from MySQL 5.0 to 5.1 and check and repair your tables.
Modifications to the handling of character sets or collations might change the character sort order,
which causes the ordering of entries in any index that uses an affected character set or collation to be
incorrect. Such changes result in several possible problems:
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