Watermark_(data_synchronization)
A Watermark for data synchronization describes an object of a predefined format which provides a point of reference value for two systems/datasets attempting to establish delta/incremental synchronization; any object in the queried data source which was created, modified, or deleted after the watermark's value will be qualified as "above watermark" and should be returned to the client requesting data.
This approach allows the client to retrieve only the objects which have changed since the latest watermark, and also enables the client to resume its synchronization job from where it left off in the event of some pause or downtime.