PolarDB:Manage the serverless feature for a cluster with defined specifications

Trigger conditions for scale-up or scale-out

• Scale-up

  PolarDB monitors the CPU utilization, memory usage, and other kernel metrics of the primary node and read-only nodes. During a monitoring cycle, the scale-up of serverless resources is triggered when one of the following conditions is met:

  • When the CPU utilization of a single node is higher than the default scale-up threshold 80% or a custom threshold, the scale-up of the CPU specifications of the node is triggered.

  • When the memory usage of a single node is higher than 90%, the scale-up of the memory specifications of the node is triggered.

  • When the specifications of a read-only node are less than half of the specifications of the primary node, the scale-up of the specifications of the read-only node is triggered. For example, if the specifications of a read-only node are 4 PCUs and the specifications of the primary node are 10 PCUs, the specifications of the read-only node are scaled up to at least 5 PCUs.

• Scale-out

  When a read-only node of a cluster is scaled in to the maximum specifications and the business workloads are still higher than the threshold for a scale-in (CPU utilization is higher than the default threshold 80% or the specified threshold), the scale-out of read-only nodes is triggered.

Trigger conditions for scale-down

When the CPU utilization of a single node is lower than the default scale-down threshold 50% or a custom threshold and the memory usage is lower than 80%, the scale-down of the node is triggered.

Configure current parameters

In the Configure Serverless-related Parameters dialog box, click Edit to the right of the Current Parameters parameter to configure the following parameters:

• Current Parameters

  • Minimum Read-only Nodes: the minimum number of read-only nodes that can be added. Valid values: 0 to 15.

  • Maximum Read-only Nodes: the maximum number of read-only nodes that can be added. Valid values: 0 to 15.

  Note

  The number of read-only nodes automatically increases or decreases within the specified range based on the actual workloads. For more information, see Scaling.

  • Minimum Resources for Single Node: the minimum number of PCUs per node in the cluster. Valid values: 0 to 16.

  • Maximum Resources for Single Node: the maximum number of PCUs per node in the cluster. Valid values: 0 to 16.

  Note

  Example: If you set the Minimum Resources for Single Node parameter to 2 PCUs and the Maximum Resources for Single Node parameter to 8 PCUs, the original resource specifications of a node in the cluster are the defined specifications plus 2 PCUs (2 CPU cores and 4 GB memory). When the business load increases, the system automatically increases the number of PCUs of the node. However, the maximum number of PCUs can only be increased to 8 (approximately equal to 8 CPU cores and 16 GB memory) based on the settings. The resource specifications of a node in the cluster can be increased to the defined specifications plus 8 PCUs (approximately equal to 8 CPU cores and 16 GB memory).

  • Read-only Column Store Nodes: the maximum number of read-only column store nodes that can be added. Valid values: 0 to 15.

    Note

    • This parameter is displayed and available for configuration only when read-only column store nodes are already added to the cluster.

    • For more information about read-only column store nodes, see IMCIs.

• Advanced Settings

  You can modify the advanced parameters based on the resource pressure of serverless clusters.

  • Scan Interval: In Sensitive mode, serverless clusters with defined specifications respond to workloads in a faster manner, which reduces the observation window and execution period of the clusters. You can select Standard or Sensitive from the Scan Interval drop-down list.

  • Maximum CPU Resources for Elastic Upgrade: the CPU scale-up threshold for the cluster. Valid values: 40% to 100%.

  • Minimum CPU Resources for Elastic Upgrade: the CPU scale-down threshold for the cluster. Valid values: 10% to 70%.

  Note

  • The maximum CPU resources must be the same as or higher than the minimum CPU resources. The difference between the maximum CPU resources and the minimum CPU resources must be equal to or larger than 30 PCUs.

  • Serverless clusters in sensitive mode respond to load changes faster than clusters in standard mode and are suitable for businesses with instantaneous load fluctuations (such as instantaneous CPU usage spikes). Such clusters are frequently scaled based on load fluctuations.

Lifecycle Policy

Create a lifecycle policy to scale the cluster at specified time points monthly, weekly, or daily within a specified time range. It allows you to scale up or out the cluster during foreseeable peak hours (such as promotions and traffic spikes) to guarantee performance, and scale back the cluster during off-peak hours to release idle resources.

1. In the Configure Serverless-related Parameters dialog box, click + Add Lifecycle Policy. Set the following parameters:

   Parameter	Valid value
   Maximum Resources for Single Node	Valid values: 0 to 16.
   Minimum Resources for Single Node	Valid values: 0 to 16. The value of the Minimum Resources for Single Node parameter must be less than or equal to the value of the Maximum Resources for Single Node parameter.
   Maximum Read-only Nodes	Valid values: 0 to 15.
   Minimum Read-Only Nodes	Valid values: 0 to 15. The value of the Minimum Read-only Nodes parameter must be less than or equal to the value of the Maximum Read-only Nodes parameter.
   Read-only Column Store Nodes	Valid values: 0 to 15. Note This parameter is displayed and available for configuration only when read-only column store nodes are already added to the cluster. For more information about read-only column store nodes, see IMCIs.
   Start/End Time	The validity period of the recurring policy.
   Policy Scheduling	The scheduling settings of the recurring policy. Valid values for the options of the Every parameter: Month: specifies the counting method of days and the days and time for execution. Positive indicates forward counting from the first day of a month. Last indicates backward counting from the last day of a month. Separate multiple days with commas (, ). Example: 1,3,5. Weekly: specifies the day and time for execution. Daily: specifies the time for execution.

   Note

   After a lifecycle policy is created, the system adjusts the serverless parameters of the cluster within the time range specified by Start/End Time based on the schedule specified by Policy Scheduling. Adjusted parameters are not automatically changed back. You can create another lifecycle policy to change back the parameters at a specified point in time. For more information, see Example.

2. (Optional) Query scheduled tasks by using one of the following methods:

   Note

   After a recurring policy is created, scheduled tasks are automatically generated based on the policy.

   • After the recurring policy is created, you can view its execution plans on the cluster details page.

     

   • Choose Task Management > Scheduled Tasks on the PolarDB console to view scheduled tasks.

     

Example

If you want to scale up 5 PCUs at 9:30 and scale down 1 PCU at 22:00 every business day (Monday to Friday) from August 1 to September 30, you can configure the settings as shown in the following figures.