In a very large cluster the Overseer is likely to be overloaded.If the same node is a serving a few other shards it can lead to OverSeer getting slowed down due to GC pauses , or simply too much of work . If the cluster is really large , it is possible to dedicate high end h/w for OverSeers
It works as a new collection admin command
This results in the creation of a entry in the /roles.json in ZK which would look like the following
If a node is designated for overseer it gets preference over others when overseer election takes place. If no designated servers are available another random node would become the Overseer.
Later on, if one of the designated nodes are brought up ,it would take over the Overseer role from the current Overseer to become the Overseer of the system