The upgrade counter is created when upgrading a server database created with a 2000.2 or earlier server.
A database upgrade occurs automatically when launching a Helix Server using a database with fewer than 1000 changelists. Otherwise, a Helix database upgrade requires running the "p4d -xu" command.
The current value for the upgrade counter can be seen with this command:
p4 counter upgrade
See the Helix Schema
to view the complete list of upgrades and their associated release.
An upgrade counter that is set to a value lower than the associated server version can prevent the server from starting. This can happen, for example, when restoring a checkpoint with a more recent version of p4d
than that which generated the checkpoint. The remedy is to use the server upgrade command "p4d -xu" to upgrade the Helix database and automatically set the upgrade counter appropriately. See the associated KB article on Upgrading a Helix Server