Recovery happens now faster, especially in a lightly loaded system, because background checkpointing has been made more frequent.
InnoDB allows now several similar key values in a UNIQUE secondary index if those values contain SQL NULLs. Thus the convention is now the same as in MyISAM tables.
InnoDB gives a better row count estimate for a table which contains BLOBs.
In a FOREIGN KEY constraint InnoDB is now case-insensitive to column names, and in Windows also to table names.
InnoDB allows a FOREIGN KEY column of CHAR type to refer to a column of VARCHAR type, and vice versa. MySQL silently changes the type of some columns between CHAR and VARCHAR, and these silent changes do not hinder FOREIGN KEY declaration any more.
Recovery has been made more resilient to corruption of log files.
Unnecessary statistics calculation has been removed from queries which generate a temporary table. Some ORDER BY and DISTINCT queries will now run much faster.
MySQL now knows that the table scan of an InnoDB table is done through the primary key. This will save a sort in some ORDER BY queries.
The maximum key length of InnoDB tables is again restricted to 500 bytes. The MySQL interpreter is not able to handle longer keys.
The default value of innodb_lock_wait_timeout was changed from infinite to 50 seconds, the default value of innodb_file_io_threads from 9 to 4.
This is a translation of the MySQL Reference Manual that can be found at dev.mysql.com. The original Reference Manual is in English, and this translation is not necessarily as up to date as the English version.