Mango supports three types of point value logging
When point value changes is the default logging setting. The point value and its time of occurrence is written to the database only if the value of the point actually changes. This setting provides the best compromise of quality of historical information vs storage space efficiency. For Numeric points, a Tolerance, or "deadband", can also be provided; the value will be logged if the absolute value of the difference between the present value and the previous value equals or exceeds the given tolerance.
The All data setting causes every point update to be saved to the database. Only use this setting if knowledge of every update is definitely required since a great deal of data can be accumulated very quickly, which over time can cause serious performance degradation.
The Do not log setting prevents any historical data for the point from being stored in the database. Please note that chart renderers typically require logged data to function properly. Only use "Do not log" when certain that the value history is not needed.
The Purge settings determine how long a point's historical values should be kept in the database. Values can be practically kept as long as necessary, but note that performance degradation may occur if the history for a given point becomes too large. (Actually performance of the system depends strongly upon the host hardware.) The purge process runs automatically every morning at 3:05am local time.