Adding or Deleting a CN in a DWS Cluster

Purpose

The number of CNs required in a cluster changes with service requirements. During peak hours, you may need to add CNs to process a large number of concurrent query requests and to avoid performance bottlenecks. During off-peak hours, you can remove idle CNs to reduce cost. CN management allows you to dynamically adjust the number of CNs in a cluster as required.

Constraints and Limitations

• This feature is supported only by clusters running version 8.1.1 or later.
• Only cluster versions 8.1.3.300 and later (excluding 8.2.0) support online CN addition, deletion, and concurrent addition of multiple CNs.

• During resource provisioning, the default number of CNs is 3. You can adjust the number of CNs based on the number of provisioned nodes. The number of CNs ranges from 2 to 20.
• Before adding a CN, ensure that the cluster is in the Available or Unbalanced state.
• Do not perform other O&M operations when adding or deleting a CN.
• Adding CNs consumes lots of CPU and I/O resources, which will greatly impact job performance. You are advised to perform this operation during off-peak hours or after services are stopped.
• If a fault occurs when you add a CN node and the rollback fails, try adding the CN again. The deletion of a CN node cannot be rolled back.
• For a CN that fails to be added, you can only retry the addition. For a CN that fails to be deleted, you can only retry the deletion. Other O&M operations are not allowed for such CNs.
• If DDL operations, such as schema and function creation, are performed during CN deletion, an error may be reported because the deleted CN cannot be found. In this case, try again.
• If one of your CNs is abnormal, you can only delete this abnormal CN. If two or more CNs are abnormal, you can delete CNs only after the CNs are recovered from faults.
• Clusters of version 9.1.1 and later support job termination.

Adding CNs

1. Log in to the DWS console.
2. Choose Cluster > Cluster List and locate the cluster to which you want to add a CN.
3. In the Operation column of the specified cluster, choose More > Manage CN > Add CN Node.
4. On the displayed page, determine whether to add a CN to a specified node. You cannot add more CNs than the number of CNs that have already been deployed.
   • If you select No, you can set Total CNs After Adjustment. The value cannot exceed the number of nodes.
     • Terminate Blocked Job:If you enable this function, you can configure automatic job termination.
     • Time Before Blocked Job Termination (s): If job termination is enabled and congestion occurs during online CN adding, the system waits for the duration you specified and then terminates congested jobs. The value can be an integer in the range 30 to 1200.
     Figure 1 Adding CNs
     

   • If you select Yes, specify the node.

     

5. Click OK.

Deleting CNs

1. Log in to the DWS console.
2. Choose Cluster > Cluster List and locate the cluster to which you want to delete a CN.
3. In the Operation column of the specified cluster, choose More > Manage CN > Delete CN Node.
4. On the displayed page, select the CN node to be deleted. After confirming that the information is correct, enter DELETE or click Auto Enter and click OK.
   • At least two CNs must be retained.
   • When deleting a CN from a multi-AZ cluster, reserve a normal CN in each AZ. Faulty CNs (if any) can be deleted.
   • Yoyu can delete a CN only if the cluster is in the Available, Degraded, or Unbalanced state.
   • A CN with an EIP cannot be deleted.
   • If there are abnormal CNs, only such CNs can be deleted.
     • If one CN is faulty, only this CN can be deleted.
     • If two or more CNs are faulty, no CN can be deleted.