The memory required for maintaining the private views of the database system monitor system monitor data is allocated from the monitor heap. Its size is controlled by the mon_heap_sz configuration parameter. The amount of memory required for monitoring activity varies widely depending on the number of monitoring applications and event monitors, the switches set, and the level of database activity. The following formula provides an approximation of the number of pages required for the monitor heap.
(number of monitoring applications + 1) *
(number of databases *
(800 + (number of tables accessed * 20) +
((number of applications connected + 1) *
(600 + (number of table spaces * 100)))))
+ (((sum of event monitor buffer sizes) * 4096) * 2)
You may need to experiment with this value, increasing it if monitor commands occasionally fail with an SQLCODE of -973, when the database manager switches are on.