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.
Watermark term is often used in Directory Synchronization software development projects.
For example, products such as Microsoft Exchange Server, Active Directory, Active Directory Application Mode (ADAM), and Microsoft Identity Integration Server 2003/ Microsoft Identity Lifecycle Manager Server 2007, as well as Cisco Unified Communications Manager or Sun Microsystems IPlanet and other LDAP-based directory products are using DirSync and consequently will consume "watermark" object to provide efficient synchronization between directories.
The DirSync control is a Lightweight Directory Access Protocol (LDAP) server extension that enables a program to search an Active Directory partition for objects that have changed.
With the first search, the program creates an empty cookie and Active Directory returns all objects that satisfy the query.