Those looking to upgrade major versions of MySQL in a production environment should test and evaluate their systems before upgrading. The ideal would be to install all software on a test machine, upgrade the MySQL installation on the test machine to MySQL 5, and then run the test machine with real data for a while to ensure there are no suprises. If all goes well on the test machine you can then move the production systems to the newer version.
Production machines should also only be upgraded to a production version of MySQL. While the beta versions of MySQL have been very stable, there are no guarantees that your application will run flawlessly on beta software.
Finally, there are upgrade notes for all versions of MySQL.
This was first published in September 2005