InnoDB now supports ALTER TABLE DROP FOREIGN KEY. You have to use SHOW CREATE TABLE to find the internally generated foreign key ID when you want to drop a foreign key.

SHOW INNODB STATUS now prints detailed information of the latest detected FOREIGN KEY and UNIQUE KEY errors. If you do not understand why InnoDB gives the error 150 from a CREATE TABLE, you can use this statement to study the reason.

ANALYZE TABLE now works also for InnoDB type tables. It makes eight random dives to each of the index trees and updates index cardinality estimates accordingly. Note that because these are only estimates, repeated runs of ANALYZE TABLE may produce different numbers. MySQL uses index cardinality estimates only in join optimization. If some join is not optimized in the right way, you may try using ANALYZE TABLE.

InnoDB group commit capability now works also when MySQL binary logging is switched on. There have to be > 2 client threads for the group commit to become active.

Changed the default value of innodb_flush_log_at_trx_commit from 0 to 1. If you have not specified it explicitly in your my.cnf, and your application runs much slower with this new release, it is because the value 1 causes a log flush to disk at each transaction commit.

Added a new global settable MySQL system variable innodb_max_dirty_pages_pct. It is an integer in the range 0 - 100. The default is 90. The main thread in InnoDB tries to flush pages from the buffer pool so that at most this many percents are not yet flushed at any time.

If innodb_force_recovery=6, do not let InnoDB do repair of corrupt pages based on the doublewrite buffer.

InnoDB startup now happens faster because it does not set the memory in the buffer pool to zero.

Fixed a bug: The InnoDB parser for FOREIGN KEY definitions was confused by the keywords 'foreign key' inside MySQL comments.

Fixed a bug: If you dropped a table to which there was a FOREIGN KEY reference, and later created the same table with non-matching data types, InnoDB could assert in dict0load.c, in function dict_load_table().

Fixed a bug: GROUP BY and DISTINCT could treat NULL values as not equal. MySQL also failed to do the next-key locking in the case of an empty index range.

Fixed a bug: Do not commit the current transaction when a MyISAM table is updated; this also makes CREATE TABLE not to commit an InnoDB transaction, even when binary logging is enabled.

Fixed a bug: We did not allow ON DELETE SET NULL to modify the same table where the delete was made; we can allow it because that cannot produce infinite loops in cascaded operations.

Fixed a bug: Allow HANDLER PREV and NEXT also after positioning the cursor with a unique search on the primary key.

Fixed a bug: If MIN() or MAX() resulted in a deadlock or a lock wait timeout, MySQL did not return an error, but returned NULL as the function value.

Fixed a bug: InnoDB forgot to call pthread_mutex_destroy() when a table was dropped. That could cause memory leakage on FreeBSD and other non-Linux Unix systems.