Tombstoned or STOPPED tablet replicas
You may notice some replicas on a tablet server are in a STOPPED state and remain on the server indefinitely. These replicas are tombstones. A tombstone indicates that the tablet server once held a bona fide replica of its tablet.
example, in case a tablet server goes down and its replicas are re-replicated elsewhere, if
the tablet server rejoins the cluster, its replicas will become tombstones. A tombstone
will remain until the table it belongs to is deleted, or a new replica of the same tablet
is placed on the tablet server. A count of tombstoned replicas and details of each one are
available on the
/tablets page of the
tablet server web UI. The Raft consensus algorithm that Kudu uses for replication requires
tombstones for correctness in certain rare situations. They consume minimal resources and
hold no data. They must not be deleted.