Heya:
I ran into similar issues with memory usage-- Notably, whenever one of our users ran one of their Big Excel Reports, the Available Memory would go to Zero, and the wheels would come off of Mango. We set our JAVAOPTS to be 10G, and those problems seem to go away.
Mango uses Monster Amounts of Memory under certain conditions-- I'd say that you 1600Meg is too small. I've got site machines running with 2 gigs of RAM, and we use the JAVAOPTS small for that. Those sites only use the Modbus datasource, a handful of metapoints, and the persistent publisher. Even that seems to use all the available memory at times, and once Java takes RAM it never give sit back..
Right now, our main machine is set up with 16 gigs of RAM, with only 174 megs free. The rest of that is JAVA, which is using 14.785 GB of RAM according to TOP.
This peaks whenever a report is ran, but then Java never gives RAM back to the OS after it's taken. Right now, our JVM free memory is about 5 gigs, but that will go to < 2 gigs if one of these big reports gets ran.
Cheers,
-Greg