mysqld_safe no longer tests for the presence of the data directory when using a relatively located server binary. It just assumes the directory is there, and fails to start up if it is not. This allows the data directory location to be specified on the command line, and avoids running a server binary that was not intended. (Bug#7249)

The naming scheme of the Windows installation packages has changed slightly:

Examples: mysql-essential-4.1.9-win32.msi, mysql-noinstall-4.1.9-win32.zip See Section 2.3, “Installing MySQL on Windows”.

The Mac OS X 10.3 installation disk images now include a MySQL Preference Pane for the Mac OS X Control Panel that enables the user to start and stop the MySQL server via the GUI and activate and deactivate the automatic MySQL server startup on bootup.

The MySQL-shared-compat Linux RPM now includes the 3.23 as well as the 4.0 libysqlclient.so shared libraries. (Bug#6342)

Seconds_Behind_Master is NULL (which means “unknown”) if the slave SQL thread is not running, or if the slave I/O thread is not running or not connected to master. It is zero if the SQL thread has caught up with the I/O thread. It no longer grows indefinitely if the master is idle.

InnoDB: Do not acquire an internal InnoDB table lock in LOCK TABLES if AUTOCOMMIT=1. This helps in porting old MyISAM applications to InnoDB. InnoDB table locks in that case caused deadlocks very easily.

InnoDB: Print a more descriptive error and refuse to start InnoDB if the size of ibdata files is smaller than what is stored in the tablespace header; innodb_force_recovery overrides this.

The MySQL server aborts immediately instead of simply issuing a warning if it is started with the --log-bin option but cannot initialize the binary log at startup (that is, an error occurs when writing to the binary log file or binary log index file).

The binary log file and binary log index file now behave like MyISAM when there is a "disk full" or "quota exceeded" error. See Section A.4.3, “How MySQL Handles a Full Disk”.

Fixed problem where running mysql_fix_privilege_tables could result in grant table columns with too-short lengths if the server character set had been set to a multi-byte character set first. (Bug#7539)

InnoDB: Fixed the critical bug if you enabled innodb_file_per_table in my.cnf. If you shut down mysqld, records could disappear from the secondary indexes of a table. Unfortunately, on Windows a new Bug#8021 was introduced. Windows users of innodb_file_per_table should put a line innodb_flush_method=unbuffered to their my.cnf or my.ini to work around 8021. (Bug#7496)

InnoDB: Fixed a bug: 32-bit mysqld binaries built on HP-UX-11 did not work with InnoDB files greater than 2 GB in size. (Bug#6189)

InnoDB: Return a sensible error code from DISCARD TABLESPACE if it fails because the table is referenced by a FOREIGN KEY.

InnoDB: Fixed a bug: InnoDB failed to drop a table in the background drop queue if the table was referenced by a FOREIGN KEY constraint.

InnoDB: Fixed a bug: if we dropped a table where an INSERT was waiting for a lock to check a FOREIGN KEY constraint, then an assertion would fail in lock_reset_all_on_table().

InnoDB: Fix a little bug: we looked at the physical size of a stored SQL NULL value from a wrong field in the index; this has probably caused no bugs visible to the user. It caused only some extra space to be used in some rare cases.

InnoDB: Use the fcntl() file flush method on Mac OS X versions 10.3 and up. Apple had disabled fsync() in Mac OS X for internal disk drives, which caused corruption at power outages.

mysqladmin password now checks whether the server has --old-passwords turned on or predates 4.1 and uses the old-format password if so. (Bug#7451)

Added a --default-character-set option to mysqladmin to avoid problems when the default character set is not latin1. (Bug#7524)

Fix a problem with truncation of FLOAT values. (Bug#7361)

Fixed a bug in PROCEDURE ANALYSE(), which did not quote some ENUM values properly. (Bug#2813)

Fixed a bug that caused incorrect results for complex datetime expressions containing casts of datetime values to TIME or DATE values. (Bug#6914)

Include compression library flags in the output from mysql_config --lib_r. (Bug#7021)

Corrected a problem with mysql_config not producing all relevant flags from CFLAGS. (Bug#6964)

Corrected a problem with mysqld_safe not properly capturing output from ps. (Bug#5878)

Fixed a bug that caused a linking failure when linking both the MySQL client library and IMAP library. (Bug#7428)

Fixed table corruption bug when using INSERT DELAYED with prepared statements.

Fixed a bug that caused microseconds to be gobbled from the string result of the STR_TO_DATE function, if there is some other specifier in the format string following %f. (Bug#7458)

Made the MySQL server accept executing SHOW CREATE DATABASE even if the connection has an open transaction or locked tables. Refusing it made mysqldump --single-transaction sometimes fail to print a complete CREATE DATABASE statement for some dumped databases. (Bug#7358)

Fixed that, when encountering a “disk full” or “quota exceeded” write error, MyISAM sometimes didn't sleep and retry the write, thus resulting in a corrupted table. (Bug#7714)

Fixed that --expire-log-days was not honored if using only transactions. (Bug#7236)

Fixed that a slave could crash after replicating many ANALYZE TABLE, OPTIMIZE TABLE, or REPAIR TABLE statements from the master. (Bug#6461, Bug#7658)