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.