Heap Memory Usage

You might have installed plug in appilcation called "log reader". This application has a process which monitors the memory level on hard disk and heap memory. if it crosses the threshold limit which was set, you (admins) will get this alert notifcation.
In order to solve this problem, You can reduce the memory levels by deleting the old process instances and also by archeving the unnecssary process models so that memory usage level will come down.

This article may provide some useful information:
forum.appian.com/.../kb-1248.html

I like to clean out process instances that are in error, clean out alerts that have been addressed, clean out process instances that have a large footprint (i.e. lots of data), ensure process to process messaging is targeting a model, etc. Once cleanup is done, I do a shutdown/startup to see how the memory free has improved.
Hope that helps!

Check the Application Server section, or CTRL+F "heap", in the following KB article for some ideas on how to address this:

forum.appian.com/.../kb-1248.html