Add or remove read-only nodes

Background

A PolarDB cluster of Cluster Edition can contain up to 15 read-only nodes. Each cluster must have at least one read-only node to ensure high availability. All nodes in a cluster use the same specifications.

Billing methods of nodes

You are charged for newly added nodes based on the following billing methods:

• If a node is added to a subscription cluster, you are charged based on the subscription billing method.
• If a node is added to a pay-as-you-go cluster, you are charged based on the pay-as-you-go billing method.

Impact of the node quantity on performance

For more information, see OLTP performance tests.

Considerations

• You can add or remove read-only nodes only when the cluster does not have pending specification changes.
• Only PolarDB for MySQL clusters allow you to add multiple read-only nodes at a time. You can add up to 15 read-only nodes to a cluster.
• Only PolarDB for MySQL clusters allow you to remove multiple read-only nodes at a time. However, you must keep at least one read-only node in the cluster to ensure high availability.
• It requires about 5 to 10 minutes to add a node. The consumed time depends on the factors such as the number of new nodes, the number of tables, and the loads of the database.
• You may experience PolarDB service interruptions for a few seconds during specification changes. During this time, you cannot perform some operations. We recommend that you change specifications during off-peak hours and make sure that your applications can automatically reconnect to the cluster.

Add a read-only node

1. Log on to the PolarDB console.
2. In the upper-left corner of the console, select the region where the cluster resides.
3. Open the Add/Remove Node dialog box by using the following methods:
   • Open the Add/Remove Node dialog box from the Clusters page.

     Find the cluster and click Add/Remove Node in the Actions column.

     
   • Open the Add/Remove Node dialog box from the Overview page of the cluster.
     • Find the cluster and click the cluster ID. The Overview page appears.
     • In the Database Nodes section, click the icon to change the display mode.
     • Click Add/Remove Node.
     
4. Select Add Node and click OK.
   
5. Click Add a read-only node, specify Switching Time, and then read and accept the terms of service. Click Buy Now.
   Note

   • If you need to add multiple nodes to your PolarDB for MySQL cluster at a time, click + Add a read-only node to add nodes one after another.
   • You can set Switching Time to Switch Now or Switch At. If you select Switch At, you can specify a point in time within 24 hours. It requires about 30 minutes to upgrade the cluster from the specified point in time.
   • You may experience PolarDB service interruptions for a few seconds during specification changes. During this time, you cannot perform some operations. We recommend that you change specifications during off-peak hours and make sure that your applications can automatically reconnect to the cluster.
6. On the Purchase page, confirm the unpaid order and click Purchase.

Remove read-only nodes

1. Log on to the PolarDB console.
2. In the upper-left corner of the console, select the region where the cluster resides.
3. Go to the Add/Remove Node dialog box by using the following methods:
   • Go to the Add/Remove Node dialog box from the Clusters page.

     Find the cluster and click Add/Remove Node in the Actions column.

     
   • Open the Add/Remove Node dialog box from the Overview page of the cluster.
     • Find the cluster and click the cluster ID. The Overview page appears.
     • In the Database Nodes section, click the icon to change the display mode.
     • Click Add/Remove Node.
     
4. Select Remove Node and click OK.
   
5. Click the icon in front of the name of the node to remove the node.
   Note

   • Only PolarDB for MySQL clusters allow you to remove multiple read-only nodes at a time. However, you must keep at least one read-only node in the cluster to ensure high availability.
   • You may experience PolarDB service interruptions for a few seconds during specification changes. During this time, you cannot perform some operations. We recommend that you change specifications during off-peak hours and make sure that your applications can automatically reconnect to the cluster.
6. Read and accept the terms of service, and then click Buy Now.
   Note After a node is removed, the system refunds fees for the remaining subscription periods or stops billing. For more information, see Configuration change fees.

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