Handling Abnormal DWS Clusters

Canceling the Read-only Status: A cluster in read-only status does not allow write operations. You can remove this status on the management console. Triggering the read-only status may be due to high disk usage, so you need to clean up the cluster data. For details, see Solution to High Disk Usage and Cluster Read-Only.
Performing a Primary/Standby Switchback: In the Unbalanced state, the number of primary instances on some nodes increases. As a result, the load pressure is high. In this case, the cluster can be operated, but the overall performance is not as good as that in a balanced state. You can perform a switchback to change the cluster status to Available.

You can cancel the read-only status of a cluster:

The read-only status can be canceled for version 1.7.2 or later.
In 8.2.0 and later versions, you can free up disk space by using DROP/TRUNCATE TABLE in a read-only cluster.

You can cancel the read-only status only when a cluster is read-only.
When a cluster is in read-only status, stop the write tasks to prevent data loss caused by used up disk space.
After the read-only status is canceled, clear the data as soon as possible to prevent the cluster from entering the read-only status again after a period of time.

Log in to the DWS console.
In the navigation pane on the left, choose Cluster > Cluster List. All clusters are displayed by default.
In the row containing the cluster whose cluster status is Read-only, click Cancel Read-only.
In the dialog box that is displayed, click OK to confirm and remove the read-only status for the cluster.

You can perform a primary/standby switchback for a cluster.

Only clusters running version 8.1.1.202 or later support primary/standby switchback.
The primary/standby switchback for a cluster interrupts services for a short period of time. The interruption duration depends on the service volume. You are advised to perform this operation during off-peak hours.

Log in to the DWS console.
Choose Cluster > Cluster List and locate the cluster whose load is unbalanced.
In the Cluster Status column of the cluster, click Fix under Unbalanced.
In the dialog box that is displayed, confirm that the service is in off-peak hours, and click Yes. A message will be displayed in the upper right corner, indicating that the switchback request is being processed.
Check the cluster status. During the switchback, the cluster status is Switching back. After the switchback, the cluster status will change to Available.

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