Mastering Active Directory - Second Edition

The High Watermark Vector (HWMV) table

The HWMV table is maintained locally by each domain controller in order to keep track of the last change from its replication partner for the given naming context (NC). As you are aware, domain controllers have three NCs: schema NCs, configuration NCs, and domain NCs. There is an HWMV table for each NC. The table contains the latest USN value it received from its replication partner for a given NC. Based on that, the domain controller decides where to start the replication process.