This alert presents the number of under-replicated ranges.
This alert is raised in a warning state when under-replicated ranges start to exist.
Under-replicated ranges: When a cluster is first initialized, the few default starting ranges
will only have a single replica, but as soon as other nodes are available, they will
replicate to them until they’ve reached their desired replication factor. If a range does not
have enough replicas, the range is said to be “under-replicated”.
CockroachDB uses consensus replication and requires a quorum of the replicas to
be available in order to allow both writes and reads to the range. The number of failures
that can be tolerated is equal to (Replication factor - 1)/2. Thus, CockroachDB requires (n-1)
/2 nodes to achieve quorum. For example, with 3x replication, one failure can be tolerated;
with 5x replication, two failures, and so on.1
References and Sources
Identify under-replicated ranges
Check out the CockroachDB documentation
for troubleshooting advice.