It doesnt work so well. The MySQL 4 libs are different than MySQL 3.x that ships with Fedora. In order to get it to work, you'll have to rebuild everything linked against mysql libs, such as php or perl dbi.
I just got it going, and you don't need to rebuild clients. (At least, so far I haven't needed to.) There's a MySQL-shared-compat RPM on the MySQL site that you're supposed to use to supply the missing library, but that didn't work for me. Instead, I knocked together a quick RPM that just repackages the files in /usr/lib/mysql from FC2's mysql-3.23.58-9, and installed that along with the MySQL-4.1.2 RPM's I built from their source RPM. After doing the update, I found that I'd lost the mysql user to run the server binary, so I had to recreate him using the command from the spec file:
useradd -M -r -d /var/lib/mysql -s /bin/bash -c "MySQL server" -u 27 mysql
(I haven't tracked that down but I'm guessing it's a bug in the %post in the spec file that doesn't handle updates cleanly.)
I had to comment out the basedir directive in /etc/my.cnf as it was no longer appropriate for this installation.
The mysql initscript starts and stops silently, instead of saying OK and FAILED, so I put a "set -x" at the top until I got it working to see which parts were working or failing. Whoever officially brings this into Fedora will need to integrate the RH initscript macros.
PHP must be happy with the old library as I can browse the old DB's with phpMyAdmin.
