Important Change: Uninstalling MySQL using the MySQL installer on Windows would delete the my.ini file. The file is no longer deleted. In addition, when a new installation is conducted, any existing cofiguration file will be renamed to myDATETIME.ini.bak during configuration. (Bug#36493)

The server printed warnings at startup about adjusting the value of the max_join_size system variable. (These were harmless, but might be seen by users as significant.) (Bug#46385)

The server crashed if evaluation of GROUP_CONCAT(... ORDER BY) required allocation of a sort buffer but allocation failed. (Bug#46080)

After an error such as a table-full condition, INSERT IGNORE could cause an assertion failure for debug builds. (Bug#46075)

An optimization that moved an item from a subquery to an outer query could cause a server crash. (Bug#46051)

Several Valgrind warnings were corrected. (Bug#46003, Bug#46034, Bug#46042)

For problems reading SSL files during SSL initialization, the server wrote error messages to stderr rather than to the error log. (Bug#45770)

The vendor name change from MySQL AB to Sun Microsystems, Inc. in RPM packages was not handled gracefully when upgrading MySQL using an RPM package. (Bug#45534)

A Windows Installation using the GUI installer would fail with:

MySQL Server 5.1 Setup Wizard ended prematurely

The wizard was interrupted before MySQL Server 5.1. could be completely installed.

Your system has not been modified. To complete installation at another time, please run
setup again.

Click Finish to exit the wizard

This was due to an step in the MSI installer that could fail to execute correctly on some environments. (Bug#45418)

Compiler warnings on Windows were fixed. (Bug#45287)

Invalid memory reads could occur using the compressed client/server protocol. (Bug#45031)

Invalid input could cause invalid memory reads by the parser. (Bug#45010)

Creating a new instance after previously removing an instance would fail to complete the installation properly because the security settings could not be applied correctly. (Bug#44428)

The server did not always check the return value of calls to the hash_init() function. (Bug#43572)

A test for stack growth failed on some platforms, leading to server crashes. (Bug#42213)

SHOW PROCESSLIST could access freed memory of a stored procedure run in a concurrent session. (Bug#38816)

During installation on Windows, the MySQL Instance Configuration Wizard window could be opened at a size too small to be usable. (Bug#38723)

make_binary_distribution did not always generate correct distribution names. (Bug#37808)

The server crashed when executing a prepared statement containing a duplicated MATCH() function call in the select list and ORDER BY clause; for example, SELECT MATCH(a) AGAINST('test') FROM t1 ORDER BY MATCH(a) AGAINST('test'). (Bug#37740)

When performing an installation on Windows using the GUI installer, the installer would fail to wait long enough during installation for the MySQL service to be installed, which would cause the installation to fail and may cause security settings, such as the root password to not be applied correctly. (Bug#30525)

If InnoDB reached its limit on the number of concurrent transactions (1023), it wrote a descriptive message to the error log but returned a misleading error message to the client, or an assertion failure occurred. (Bug#18828)

See also Bug#46672.

Installation of MySQL on Windows would fail to set the correct location for the character set files, which could lead to mysqld and mysql failing to initialize properly. (Bug#17270)