Rescaling a Cluster

You may need to change the size and structure of your ClickHouse® cluster at some point. Clicking the Rescale menu item displays this dialog:

Figure 1 - The Rescale Cluster dialog

The current properties of your cluster are shown on the left side; you can enter new values or select a new node type on the right. In Figure 4 above, the number of replicas has increased from 2 to 4, so the dialog gives you the option of selecting availability zones for the new replicas. In addition, the text under the Desired Node Size section includes a Storage link that takes you to the ACM panel to edit the storage policy. (See Configuring Storage for the details.)

At the bottom of the dialog is an estimate of the monthly cost of your rescaled cluster, including the difference between your current configuration and the new one.

Click OK to rescale the cluster with the new values. As you would expect, the rescaling time varies with the size of the cluster, as each node is rescaled individually.

The rescaling operation takes place one node at a time, so the impact of rescaling should have a minimal impact on the performance of your applications. (Assuming your cluster has more than one replica, of course.)

NOTE: Rescaling a cluster resets its activity schedule to ALWAYS ON. If your cluster is using the RESCALE ON SCHEDULE activity schedule, you’ll see this confirmation message:

Figure 2 - The Rescale Confirmation dialog

(You’ll see similar messages for STOP WHEN INACTIVE or STOP ON SCHEDULE.) If you rescale the cluster, you’ll need to recreate its activity schedule. See Configuring Activity Schedules for all the details.