(Note: Please feel free to make corrections/updates as needed. This is primarily from my experiences with MySQL and uPortal since 2002)
USING MYSQL WITH UPORTAL
MySQL is a free, open source database, available for download at http://dev.mysql.com/ (more information can also be found at http://www.mysql.com) - also at this address, the JDBC driver for MySQL, Connector/J, can be downloaded. The Generally Available (GA) release is usually what is desired - it is best to use this instead of the Beta versions. As of this writing (5/23/05), the latest GA version of the database is 4.1.12 and is available for Windows, Mac OSX, Unix (Solaris), most flavors of Linux, and HP-UX, to name a few. The latest GA Connector/J is 3.1.8a, available in a .zip and a .tar.gz. For information on how to create a database in MySQL or create the tables, you will need to refer to the documentation that came with the version of MySQL you have decided to use. There are links to MySQL documentation as well on the above site.
UPORTAL CONFIGURATION
Before using MySQL with uPortal, several uPortal properties files need to be altered for MySQL. These include:
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When the MySQL tables are created, they will be the MySQL default type - as of this writing (5/23/05), that's MyISAM. These tables are NOT transaction safe, which means that if an error occurs, like a communications/network error, the tables cannot be rolled back to their previous state. There are places in the uPortal code where if such a problem occurs, the transaction is programmed to roll back to its previous state - but if the tables cannot accomodate this, an error about not being able to roll back the tables will be entered into portal.log, and the account will be unusable after that point. To avoid this, use transaction safe tables, which MySQL provides support for, in terms of either BDB (Berkeley database) or InnoDB tables. As of 4.0.5, support for InnoDB tables is included with MySQL; previous to that, it was an extra download.
SOME OTHER NOTES
Assuming you've got the needed statements for InnoDB tables in your my.cnf file, you can change already-created MyISAM tables to Innodb tables with an ALTER TABLE statement - see the documentation for the exact syntax. Or, you can drop all your tables and re-create them with "TYPE=InnoDB" on your CREATE TABLE statements. If you're not sure about using TST (Transaction Safe Tables), do some reading on the MySQL site (http://www.mysql.com) about some of the companies and organizations that are currently using them - for instance, Slashdot.org uses MySQL InnoDB tables to handle their more than 100,000 hits per week.
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