There are two methods for configuring history retention. One is on a per point basis in the Point Service using the Keep values within last setting. The other is to define a minimum retention period for the VHS itself using the optional service configuration keyword MINIMUM_EXPIRE_DAYS.
MINIMUM_EXPIRE_DAYS defines the number of days that values will be stored in the VHS. It works in conjunction with the value history period of each point. If a point is configured with a longer retention period than the VHS, the point setting will take precedence. If both settings are configured, the longer of the two retention periods will take precedence.
In the example below, Point_01 is configured for an retention period of 60 days, but the data will be retained in the VHS for 365 days since the VHS retention period is longer. The data for Point_03 will be retained for 730 days, since its retention period is equal to that of the VHS. The data for all points will be retained for 1460 days in the archiving VHSDEST.
The minimum expiration period for the service can be changed. If it is reduced, the VHS will remove data for points that exceed the specified period (for applicable tags).
|
|
|
