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.
     1. Find the cluster and click the cluster ID. The Overview page appears.
     2. In the Database Nodes section, click the icon to change the display mode.
     3. 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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