You can define foreign key constraints on InnoDB tables. An example: FOREIGN KEY (col1) REFERENCES table2(col2).

You can create data files larger than 4GB in those file systems that allow it.

Improved InnoDB monitors, including a new innodb_table_monitor which allows you to print the contents of the InnoDB internal data dictionary.

DROP DATABASE now works also for InnoDB tables.

Accent characters in the default character set latin1 are ordered according to the MySQL ordering.

NOTE: If you are using latin1 and have inserted characters whose code is > 127 to an indexed CHAR column, you should run CHECK TABLE on your table when you upgrade to 3.23.43, and drop and reimport the table if CHECK TABLE reports an error!

InnoDB calculates better table cardinality estimates.

Change in deadlock resolution: in .43 a deadlock rolls back only the SQL statement, in .44 it rolls back the whole transaction.

Deadlock, lock wait timeout, and foreign key constraint violations (no parent row, child rows exist) now return native MySQL error codes 1213, 1205, 1216, 1217, respectively.

A new my.cnf parameter innodb_thread_concurrency helps in performance tuning in high concurrency environments.

A new my.cnf option innodb_force_recovery helps you in dumping tables from a corrupted database.

A new my.cnf option innodb_fast_shutdown speeds up shutdown. Normally InnoDB does a full purge and an insert buffer merge at shutdown.

Raised maximum key length to 7000 bytes from a previous limit of 500 bytes.

Fixed a bug in replication of AUTO_INCREMENT columns with multiline inserts.

Fixed a bug when the case of letters changes in an update of an indexed secondary column.

Fixed a hang when there are more than 24 data files.

Fixed a crash when MAX(col) is selected from an empty table, and col is a not the first column in a multi-column index.

Fixed a bug in purge which could cause crashes.