ClickHouse cluster structure

A ClickHouse cluster is a logical group of devices that possess all accumulated normalized KUMA events. It consists of one or more logical shards.

A shard is a logical group of devices that possess a specific portion of all normalized events accumulated in the cluster. It consists of one or more replicas. Increasing the number of shards lets you do the following:

• Accumulate more events by increasing the total number of servers and disk space.
• Absorb a larger stream of events by distributing the load associated with an influx of new events.
• Reduce the time taken to search for events by distributing search zones among multiple devices.

A replica is a device that is a member of a logical shard and possesses a single copy of that shard's data. If multiple replicas exist, it means multiple copies exist (the data is replicated). Increasing the number of replicas lets you do the following:

• Improve high availability.
• Distribute the total load related to data searches among multiple machines (although it's best to increase the number of shards for this purpose).

A keeper is a device that participates in coordination of data replication at the whole cluster level. At least one device per cluster must have this role. The recommended number of the devices with this role is 3. The number of devices involved in coordinating replication must be an odd number. The keeper and replica roles can be combined in one machine.