Recovery happens now faster, especially in a lightly loaded system, because background checkpointing has been made more frequent.
InnoDB now permits several similar key
values in a
UNIQUE secondary index if those
values contain SQL
NULL values. Thus the
convention is now the same as in
InnoDB gives a better row count estimate
for a table which contains
FOREIGN KEY constraint,
InnoDB is now case-insensitive to column
names, and in Windows also to table names.
InnoDB permits a
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
these silent changes do not hinder
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 now run much faster.
MySQL now knows that the table scan of an
InnoDB table is done through the primary
key. This saves 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.