By default, if the action involves a programatic check, such as a system mail rule, the code to perform that check is cached as well. On a server with many such monitors, the memory required to cache the code to perform the monitoring may be so big that normal server operations are affected.
To prevent caching of the compute objects for monitors use the following Notes.ini variable, Dont_Cache_Monitor_Formulas=1.
This greatly reduces memory usage at a small cost in processing power.
SPR# PMIA69WPQY