Thanks for the suggestions, everyone. This is what I have so far:
I require an open source DBMS because I want to avoid being locked
into a particular vendor, especially one that will send me a big bill.
That leaves me with MySQL, PostgreSQL (my preference), Firebird, and
possibly Berkeley DB (if I'm willing to part with SQL). I posted a
message on comp.databases.berkeley looking for real world examples
where Berkeley is being used in a heavily accessed CMS, but have
gotten no reply. Firebird is looking very attractive too. At the
moment, a commercial license for MySQL with all the support bells and
whistles is an impossibility since I'm already paying for other
requirements. At this time, I can't immediately choose to GPL my app.
I learned that even PostgreSQL's UTF-8 comes with caveats. I've also
learned that MySQL will choke on heavy concurrent writes. Unlike in my
Slashdot.org and catch27.com examples, my site would get as many
writes as it does reads - all with heavy concurrency (a lot of
inserts, deletes, and updates).
There won't be any chat functions, but it's not like I'd store those
in an DB anyway; however there will be message posts. If you think of
the project as being a hybrid of online magazine and web-based
BBS/social networking, then you can imagine the different data types I
will be using. There will be some number crunching, but it's mostly
UTF-8 encoded English text with scattered non-English words thrown in.
There will also be user-submitted pictures (JPEGs, GIFs, PNGs).
I'm content to stick with PostgreSQL providing that it can handle
heavy concurrent writes. I'll explore Firebird more too. Wayne
Conrad's comment about his own use of PostgreSQL has me pretty
optimistic, as does the Proximity multimedia archival case study at
postgresql.org. That FeedLounge.com blog Chris linked was definitely
an eye-opener.
Regards,
Anthony