Well, it depends on a lot of parameters. A short answer is:
use bogus data to test your setup. Test it to its limits,
and find out where you can expect problems.
in reply to When is a flat file DB not enough?
What kind of limits can you think of?
- Size limits. Maybe 'more' hardware can help out. Maybe
you can compress the data with gzlib or the like.
- Speed limits. Maybe 'more' hardware as well. Maybe
a migration to another DB system might help (BerkeleyDB
did wonders for me).
- Usability limits. Think about multiple users accessing
at the same time. BerkeleyDB or file locking scemes can help.
RDMBS like oracle/mysql have the tendency to solve problems
at all three levels.....
Hope this helps,
"We are not alone"(FZ)