Problem update:

I stopped the client application that uses the small database in ODS 11.1
(about 4MB in size).
With this action, the memory usage of fbserver.exe dropped to normal values.
I started the client again, and we'll see what happens.

I have another installations where fbserver.exe is also consuming more
memory than usually. I tried to get some useful info with the monitoring
tables, but found nothing special there. What do I have to look for in order
to find out, why my client blocks this amount of memory in the server?

Thank you guys.

Joja