Time in seconds between attempts to clear unused performance history data. Performance history can take a lot of memory. If the manager fails to delete entries in the perfControlTable, the memory will never be recovered. To avoid this, the agent periodically removes entries which have not been used recently. This is done through a mark-and-sweep method, as follows: - each perfControEntry has a mark - reading perfDataEntries sets the mark on associated perfControlEntry - the sweeper sweeps all perfControlEntries periodically. If an entry is not marked, it is deleted. If an entry is marked, it is unmarked, and will be deleted in the next sweep, if not used (marked) before. This value is volatile