Configuring Compute-Compute Separation

This guide walks you through provisioning child instances for an existing ClickHouse Private cluster. Compute-compute separation lets you run multiple independent compute groups against a shared dataset, each with its own sizing and endpoint.

For a conceptual overview, see Compute-Compute Separation.

Prerequisites

• A running ClickHouse Private cluster to serve as the parent (this guide uses default-xx-01)

• The ClickHouse operator installed with the compute-compute separation feature flag enabled:

  --set operator.featureFlags.privateComputeSeparationEnabled="true"

  If the operator was installed without this flag, upgrade it with the flag set to true before proceeding.

• Access to the Helm registry and the onprem-clickhouse-cluster chart

1. Identify the Parent Cluster

Before creating a child, note the parent cluster’s name and namespace. The parent must be in a running state – children cannot be provisioned if the parent is stopped, terminated, or idled.

For a cluster named default-xx-01, the defaults are:

2. Create a Child Instance

Deploy a new ClickHouseCluster using the same Helm chart you used for the parent, adding the parentCluster values to link it:

helm install default-xx-02 oci://$HELM_REGISTRY/helm/onprem-clickhouse-cluster \
    --version=$CR_HELM_TAG \
    --namespace ns-default-xx-02 \
    --create-namespace \
    --set-json='parentCluster.name="c-default-xx-01"' \
    --set-json='parentCluster.namespace="ns-default-xx-01"' \
    --set-json="server.replicas=$SERVER_REPLICAS" \
    --set-json="server.podPolicy.resources.requests.cpu=\"$SERVER_CPU\"" \
    --set-json="server.podPolicy.resources.requests.memory=\"$SERVER_MEMORY\"" \
    --set-json="server.podPolicy.resources.limits.cpu=\"$SERVER_CPU\"" \
    --set-json="server.podPolicy.resources.limits.memory=\"$SERVER_MEMORY\""

The child instance will:

• Share the parent’s ClickHouse Keeper ensemble (no separate Keeper deployment needed)
• Share the parent’s S3 data prefix
• Run its own ClickHouse Server pods with independent resource allocations
• Expose its own Kubernetes Service endpoint

3. Create a Read-Only Child (Optional)

To create a child that can query data but cannot write to it, add the isReadonly flag:

helm install default-xx-03 oci://$HELM_REGISTRY/helm/onprem-clickhouse-cluster \
    --version=$CR_HELM_TAG \
    --namespace ns-default-xx-03 \
    --create-namespace \
    --set-json='parentCluster.name="c-default-xx-01"' \
    --set-json='parentCluster.namespace="ns-default-xx-01"' \
    --set-json='isReadonly=true' \
    --set-json="server.replicas=$SERVER_REPLICAS" \
    --set-json="server.podPolicy.resources.requests.cpu=\"$SERVER_CPU\"" \
    --set-json="server.podPolicy.resources.requests.memory=\"$SERVER_MEMORY\"" \
    --set-json="server.podPolicy.resources.limits.cpu=\"$SERVER_CPU\"" \
    --set-json="server.podPolicy.resources.limits.memory=\"$SERVER_MEMORY\""

Read-only children are suitable for reporting, dashboards, or analytics workloads where write access is unnecessary.

4. Verify the Child Instance

After the child is deployed, verify it is running:

kubectl get clickhousecluster -n ns-default-xx-02

Connect via the child’s own service endpoint:

kubectl port-forward svc/c-default-xx-02-server-any 9000:9000 -n ns-default-xx-02
clickhouse client --host localhost --port 9000 --password $PASSWORD

Run a query to confirm data access:

SELECT count() FROM system.tables;

Limitations

1. Parent must be running. You cannot provision child instances if the parent instance is stopped, terminated, or idled. The parent must be in a running state because children depend on the parent’s Keeper ensemble and shared data configuration.

2. Delete children before the parent. You must delete all child instances before deleting the parent cluster. Attempting to delete a parent with active children will fail.

3. Password resets apply to the parent. Password resets cannot be performed on child instances. To reset the password for a child instance, reset it on the parent instance instead. See how-to/reset-passwords.md.