I updated MySQL from 3.23.28 (shipped with Redhat 9) to 4.0.17 last week so that I could install Zen Cart.
The chatter on the net said that this upgrade is a little more eventful than it ought to be, and so it is. The first hassle is that many many other applications are set to require a specific version of the .so files, so that if you’re unlucky you could have to recompile half your website, if you can. To their very great credit, the MySQL folks have dealt with this. There’s a version of MySQL-clent on the MySQL site which includes all the back-level headers so things like PHP will keep working.
Unfortunately, nothing actually did keep working. I ran rpm -U and restarted MySQLd, and nothing would connect. (note that this included the mysql command line app, although mysql –version returned the new and correct version number I just couldn’t log on.) Well, after poking and prodding for a while I decided to gasp bounce the system. It worked. When the box came back up, MySQL was once again dispensing wisdom and jollity to the world.
Naturally I choose to believe that there was something I didn’t know enough to do, rather than that you actually had to reboot. However, that’s what I had to do, and it could be a nice shortcut for someone who’s not a purist.