PolarDB allows you to temporarily add a specific number of nodes to a cluster. When the specified restore time is reached, the number of nodes in the cluster is automatically restored to the original value. You can temporarily add nodes to a subscription PolarDB cluster to meet your business requirements during peak hours.
Prerequisites
A subscription PolarDB cluster is created.
You do not have pending orders about the cluster for renewing nodes or temporarily adding nodes.
Usage notes
You cannot temporarily delete nodes.
When PolarDB temporarily adds nodes to or restores the number of nodes in a cluster, transient connections to the cluster may occur. Make sure that your application is configured to automatically reconnect to your cluster.
The restore time must be at least one day before the expiration date of a cluster. For example, if a cluster expires on January 10, the restore time must be January 9 or earlier.
You cannot change the configurations or perform a temporary cluster upgrade for a cluster to which nodes are temporarily added. You can convert temporarily added nodes into permanent nodes for a cluster. For more information, see the "Convert temporarily added nodes into permanent nodes" section of this topic.
You can manually add nodes for a running cluster to which nodes are temporarily added. For more information, see Add or remove read-only nodes.
When you temporarily add nodes, the restore time must be at least 1 hour later than the current time. We recommend that you set the restore time to a value within 14 days from the current time.
After you temporarily add nodes to a cluster, if the cluster still does not meet your business requirements or you want to extend the restore time, you can temporarily add nodes for another time before the original restore time is reached. The restore time specified when you temporarily add nodes for the second time cannot be earlier than that specified when you temporarily add nodes for the first time.
Convert temporarily added nodes into permanent nodes
If you want to maintain the number of nodes in a cluster to which nodes are temporarily added, you can convert temporarily added nodes in the running cluster into permanent nodes. This way, the number of nodes in the cluster does not decrease when the restore time is reached. To convert temporarily added nodes into permanent nodes, perform the following operations: In the Add/Remove Node dialog box, select Add Node. On the Upgrade/Downgrade page, click Add Read-only Node to increase the number of permanently added nodes to match the number of temporarily added nodes.
This operation does not affect your business.
If you scale up the storage of a cluster to which nodes are temporarily added, the temporarily added nodes are automatically converted into permanent nodes.
Separately change the specifications of the primary node and read-only nodes
You can add read-only nodes that have specifications different from the primary node based on your business requirements.
Limits
An Enterprise Edition cluster contains at least one primary node and up to 15 read-only nodes. A Standard Edition cluster contains at least one primary node and up to eight read-only nodes.
Make sure that the specifications of new read-only nodes do not significantly differ from the specifications of the primary node.
The memory size of a new read-only node must be at least half of the memory size of the primary node.
The number of CPU cores of a new read-only node must have the following mapping relationships with the number of CPU cores of the primary node.
CPU cores of the primary node
Minimum CPU cores of a read-only node
2
2
4
4
8
4
16
8
32
16
64
32
88
32
Each cluster must contain at least one read-only node that has the same specifications as the primary node.
The specifications of the read-only nodes that serve as hot standby nodes must be the same as the specifications of the primary node. For information about hot standby nodes, see Configure hot standby nodes.
For read-only column store nodes, we recommend that you use specifications higher than the specifications of the primary node. For more information, see Add a read-only column store node.
PolarDB clusters of Multi-master Cluster (Database/Table) Edition are not subject to the preceding limits.
Billing rules
The price of temporarily added nodes is 1.5 times the fee difference of a cluster before and after nodes are temporarily added. For example, the restore time of temporarily added nodes is N days from the current time. You can calculate the price of temporarily added nodes by using the following formula:
Price of temporarily added nodes = (Monthly subscription fee after node adding - Monthly subscription fee before node adding)/30 × 1.5 × N.
Procedure
Log on to the PolarDB console.
In the left-side navigation pane, click Clusters.
In the upper-left corner, select the region in which the cluster is deployed.
On the Clusters page, find the cluster to which you want to temporarily add nodes.
Access the Add/Remove Node dialog box by using one of the following methods:
Access the Add/Remove Node dialog box from the Clusters page.
Find the cluster that you want to manage and choose More > Add/Remove Node in the Actions column.
Access the Add/Remove Node dialog box from the Basic Information page of the cluster.
Find the cluster that you want to manage and click the cluster ID to go to the Basic Information page.
In the Database Nodes section, click Add/Remove Node.
In the Add/Remove Nodes dialog box, select Temporarily Add Node and click OK.
NoteThe Temporarily Add Node parameter is available only for subscription clusters.
In the dialog box that appears, configure parameters described in the following table.
Parameter
Description
Node
The number of nodes in the cluster after you temporarily add nodes.
NoteMake sure that the number of read-only nodes in the cluster is the same as the number of primary nodes. You can specify a custom number of temporarily added nodes.
Restore Time
The restore time for the temporarily added nodes.
NoteAfter you temporarily add nodes to a cluster, if the cluster still does not meet your business requirements or you want to extend the restore time, you can temporarily add nodes for another time before the original restore time is reached. The restore time specified when you temporarily add nodes for the second time cannot be earlier than that specified when you temporarily add nodes for the first time.
The restore time cannot be changed after it is specified. When you temporarily add nodes, the restore time must be at least 1 hour later than the current time. We recommend that you set the restore time to a value within 14 days from the current time.
The restore time must be at least one day before the expiration date of a cluster.
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