Scale a PolarDB for PostgreSQL cluster up or down by adding or removing read-only nodes from the console. Before you begin, review the capacity limits, constraints, and expected impact for your cluster type.
Cluster capacity limits
The maximum number of nodes depends on your cluster type.
Centralized clusters (Enterprise Edition or Standard Edition):
| Edition | Primary nodes | Read-only nodes |
|---|---|---|
| Enterprise Edition | 1 | Up to 15 |
| Standard Edition | 1 | Up to 7 |
Centralized clusters use an active-active failover mechanism to maintain high availability during role transitions.
Distributed clusters: Must have at least 1 compute node and 1 data node. New nodes must have the same specifications as existing compute or data nodes.
Read-only nodes with different specifications
For centralized clusters (Enterprise Edition or Standard Edition), read-only nodes do not have to match the primary node specifications. The following constraints apply:
At least one read-only node in the cluster must have the same specifications as the primary node.
The memory of a new read-only node must be at least half the memory of the primary node.
CPU cores must meet the minimum mapping relative to the primary node:
| Primary node CPU cores | Minimum CPU cores for read-only node |
|---|---|
| 2 | 2 |
| 4 | 4 |
| 8 | 4 |
| 16 | 8 |
| 32 | 16 |
| 64 | 32 |
| 88 | 32 |
During a primary/read-only node failover, a read-only node with different specifications cannot be promoted to primary.
For distributed clusters, all nodes must have the same specifications. Mixed-specification nodes are not supported.
Billing
New nodes follow the same billing method as the cluster:
Subscription clusters: new nodes are billed on the subscription method.
Pay-as-you-go clusters: new nodes are billed on the pay-as-you-go method.
When you remove a node, the system issues a refund for the remaining subscription period or stops billing immediately for pay-as-you-go nodes. Storage fees are based on actual usage and are not affected by the number of nodes.
For details, see Configuration change fees and Billable items.
Expected impact
Review the expected impact before proceeding.
| Cluster type | Operation | Impact |
|---|---|---|
| Centralized | Add node | ~5 minutes; no impact on database operations |
| Centralized | Remove node | Connections to the removed node are briefly disconnected; other nodes are unaffected |
| Distributed | Add compute or data node | Services blocked for 1 minute due to the lock mechanism |
| Distributed | Remove compute node | Connections to the removed node are briefly interrupted; other nodes are unaffected |
| Distributed | Remove data node | Data is automatically migrated in the background; migration time is proportional to data volume; CPU and I/O usage up to 20% |
To minimize impact:
Add or remove nodes during off-peak hours or maintenance windows.
Add or remove one node at a time. To change multiple nodes, repeat the operation separately for each node.
Make sure your applications support automatic reconnection before removing any node.
Add nodes
Centralized cluster
PolarDB for PostgreSQL centralized clusters are clusters whose database engine is Enterprise Edition or Standard Edition.
Log on to the PolarDB console. In the left-side navigation pane, click Clusters. Select the region where your cluster resides, then find the cluster.
Verify that no specification change tasks are in progress on the cluster before continuing.
Go to the Add/Remove Node page using one of the following methods:
Click the cluster ID. On the Basic Information page, click Add/Remove Node in the Database Nodes section.
Select Add Node and click OK.
Click + Add a Read-only Node and configure the Switching Time:
To add a read-only node with different specifications, make sure at least one existing read-only node has the same specifications as the primary node. To add multiple nodes, click + Add a read-only node again for each additional node.
Option Description Switch Now The node is added immediately after you confirm the order. Switch At Specify a time within the next 24 hours. The node is added within 30 minutes after the specified time. View or cancel scheduled tasks on the Scheduled Tasks page. For details, see View or cancel a scheduled task. Complete payment based on your billing method:
Pay-as-you-go: Read the terms of service and click Buy Now.
Subscription: Read the terms of service, click Buy Now, then confirm the order and payment method on the Purchase page and click Subscribe.
Distributed cluster
Log on to the PolarDB console. In the left-side navigation pane, click Clusters. Select the region where your cluster resides, then click the cluster ID to go to the Basic Information page.
Verify that no specification change tasks are in progress on the cluster before continuing.
In the Configurations section, click Add Node.
Click + Add a Node and configure the Switching Time:
Option Description Switch Now The node is added immediately after you confirm the order. Switch At Specify a time within the next 24 hours. The node is added within 30 minutes after the specified time. View or cancel scheduled tasks on the Scheduled Tasks page. For details, see View or cancel a scheduled task. Complete payment based on your billing method:
Pay-as-you-go: Read the terms of service and click Buy Now.
Subscription: Read the terms of service, click Buy Now, then confirm the order and payment method on the Purchase page and click Subscribe.
Remove nodes
Make sure your applications support automatic reconnection before removing any node. Removing a node causes brief connection interruptions to that node.
Centralized cluster
PolarDB for PostgreSQL centralized clusters are clusters whose database engine is Enterprise Edition or Standard Edition.
Log on to the PolarDB console. In the left-side navigation pane, click Clusters. Select the region where your cluster resides, then find the cluster.
Verify that no specification change tasks are in progress on the cluster before continuing.
Go to the Add/Remove Node page using one of the following methods:
Click the cluster ID. On the Basic Information page, click Add/Remove Node in the Database Nodes section.
Select Delete Node and click OK.
Click the - symbol next to the node you want to remove. Configure the Switching Time:
A cluster can only have one primary node. To maintain high availability, keep at least one read-only node in the cluster.
Option Description Switch Now The node is removed immediately after you confirm the order. Switch At Specify a time within the next 24 hours. The node is removed within 30 minutes after the specified time. View or cancel scheduled tasks on the Scheduled Tasks page. For details, see View or cancel a scheduled task. Complete payment based on your billing method:
Pay-as-you-go: Read the terms of service and click Buy Now.
Subscription: Read the terms of service, click Buy Now, then confirm the order and payment method on the Purchase page and click Subscribe.
Distributed cluster
Log on to the PolarDB console. In the left-side navigation pane, click Clusters. Select the region where your cluster resides, then click the cluster ID to go to the Basic Information page.
Verify that no specification change tasks are in progress on the cluster before continuing.
In the Configurations section, click Delete Node.
Click the - symbol next to the node you want to remove. Configure the Switching Time:
A distributed cluster must always have at least one compute node and one data node.
Option Description Switch Now The node is removed immediately after you confirm the order. Switch At Specify a time within the next 24 hours. The node is removed within 30 minutes after the specified time. View or cancel scheduled tasks on the Scheduled Tasks page. For details, see View or cancel a scheduled task. Complete payment based on your billing method:
Pay-as-you-go: Read the terms of service and click Buy Now.
Subscription: Read the terms of service, click Buy Now, then confirm the order and payment method on the Purchase page and click Subscribe.
API reference
| Operation | Description |
|---|---|
| CreateDBNodes | Adds read-only nodes to a PolarDB cluster |
| DeleteDBNodes | Removes read-only nodes from a PolarDB cluster |
| ModifyDBNodesClass | Changes the specifications of nodes in a PolarDB cluster |
| ModifyDBNodeClass | Changes the specifications of a node in a PolarDB cluster |
| RestartDBNode | Restarts a node in a PolarDB cluster |