PolarDB：Auto scaling

Prerequisites

• Your cluster runs PolarDB for MySQL 5.6. Other versions of PolarDB for MySQL clusters support the serverless feature and can be automatically scaled after the serverless feature is enabled. For more information about the serverless feature, see Overview.

• Your cluster is a PolarDB for MySQL Cluster Edition cluster. This feature is unavailable for a Multi-master Cluster (Database/Table). For more information about the two cluster editions, see Editions.

• No cluster configuration change tasks are being performed in the PolarDB cluster.

Billing

PolarDB for MySQL clusters that use the pay-as-you-go and subscription billing methods support the auto scaling feature.

Pay-as-you-go

Pay-as-you-go clusters are charged on an hourly basis. After you change the configurations of a pay-as-you-go cluster, the cluster is charged based on the new price per hour.

Subscription

The billing rules for manual scaling and automatic scaling are the same. For more information, see Configuration change fees.

Refunds for cluster downgrade

When the specifications of a subscription cluster exceed your business requirements and your account has the configuration downgrade privilege, you can downgrade the configurations of the cluster in real time. For more information about the refund policy, see

Rules for unsubscribing from resources.

Limits

• You can upgrade or downgrade only clusters. You cannot upgrade or downgrade a single node in a cluster.

• When you upgrade or downgrade a cluster, data stored in the cluster is not affected.

• During the upgrade or downgrade process, your applications are temporarily disconnected from the cluster for no more than 30 seconds. We recommend that you upgrade or downgrade your cluster during off-peak hours and make sure that your applications are configured with the automatic reconnection mechanism.

• A cluster scale-out or scale-in has minor impacts on the primary node of a PolarDB cluster. However, the scale-out or scale-in degrades the performance of read-only nodes in the cluster. As a result, the read-only nodes require more time to handle requests during the scale-out or scale-in process.

Procedure

1. Log on to the PolarDB console.

2. In the upper-left corner, select the region where the cluster to which you want to connect is deployed.

3. On the Clusters page, find the cluster that you want to manage and click the cluster ID.

4. On the Basic Information page, click Settings in the upper-right corner of the Database Nodes section.

   

5. In the dialog box that appears, configure the following parameters. The following table describes the parameters.

   Parameter	Description
   Auto Scaling-out	Specifies whether to enable the auto scaling feature.
   Observation Period	If the CPU utilization reaches the specified threshold during the observation period, PolarDB automatically adds nodes or upgrades the specifications of your cluster when the observation period ends. The system determines the scaling method based on the inbound read and write requests. The minimum observation period is 5 minutes, and the time required to complete a scaling activity is 10 minutes. Therefore, auto scaling requires at least 15 minutes to take effect. For example, if the observation period is 5 minutes and the time required to complete a scaling activity is 10 minutes, you must wait 15 minutes before you can check the scaling result. Note The scale-in observation window is equal to the observation window plus 10 minutes. For example, if the observation window is set to 30 minutes, the scale-in observation window is 40 minutes.
   CPU Usage	The threshold that is used to trigger automatic scale-up. If the CPU Usage is greater than or equal to the specified threshold, automatic scale-up is triggered.
   Maximum Specification	The maximum specifications to which the system can upgrade the cluster. After an automatic scale-up is triggered, the system scales up your PolarDB cluster to the maximum specifications in small increments. For example, the CPU specification can be upgraded from 4 cores to 8 cores, and then to 16 cores until the upper limit is reached.
   Maximum Number of Read-only Nodes	The maximum number of read-only nodes that can be automatically added to the cluster. After an auto scaling is triggered, the system adds one or two read-only nodes each time until the specified upper limit is reached. Note The nodes that are automatically added are associated with the default endpoint of your cluster. If you use a custom endpoint, specify whether these nodes are automatically associated with the endpoint by using the Automatically Associate New Nodes parameter. For more information about how to configure the Automatically Associate New Nodes parameter, see Configure PolarProxy. If you want the system to perform only scale-up and no scale-out, set this parameter to the current number of read-only nodes of the cluster. During a scale-up, transient disconnections occur on all nodes of the cluster. This does not occur during a scale-out.
   Auto Scaling-in	Specifies whether to enable automatic scale-back. Note After automatic scale-back is enabled, if the cluster is not in the quiescent period and the average CPU utilization of automatically scaled nodes remains at less than 30% for more than 99% of the scale-in observation window (the observation window plus 10 minutes), the cluster is scaled back tier-by-tier to the original specifications.
   Quiescent Period	The minimum interval between two scaling activities. During a quiescent period, PolarDB monitors the resource usage of a cluster but does not trigger scaling activities. If a quiescent period and an observation period end at the same time and the CPU utilization reaches the threshold within the observation period, PolarDB automatically triggers auto scaling.

6. Click OK.

You can disable auto scaling at any time. If the cluster has been automatically scaled up/out but has not been scaled back when you disable auto scaling, the cluster is not scaled back to its original configurations.