The "cache time window" (see the figure below) decides whether a UDR shall be removed from the cache or not. The maximum number of days to store a UDR in the cache is retrieved from the setting Max Cache Age (days) each time a new batch file is processed (and the age of the UDRs is calculated). The "cache time window" will be moved forward and old UDRs will be removed.
Calculation of the UDR age can be done in two ways:
Using the latest indexing field (timestamp) of a UDR that is included in the previously processed batch files.
Using system time.
The following figure illustrates the difference:
If the system has been idle for an extended period of time, there will be a "delay" in time. So when a new batch file is processed, and if the system time is used for UDR age calculation, the "cache time window" will be moved forward with the delay included, and this might result in all UDRs being removed from the cache, as shown in the figure above. The consequence of this is that the improperly removed UDRs will be considered non-duplicates and, hence, might be handled even though they still are duplicates.
If the indexing field is used instead, a more proper calculation will be done, since the "system delay time" will be excluded. In this case, only UDR 1 and UDR 2 will be removed.