Adjust the minimum and maximum RDS Capacity Units (RCUs) for your RDS SQL Server Serverless instance to handle traffic spikes without over-provisioning, or to reduce costs during low-traffic periods.
Alibaba Cloud will stop selling RDS SQL Server Serverless instances on November 3, 2025, and will stop providing related technical support on June 1, 2026. Technical support includes new feature iterations and fixes for technical issues. Convert your RDS SQL Server Serverless instances to pay-as-you-go instances as soon as possible.
How it works
RDS SQL Server Serverless instances measure performance in RCUs. The instance automatically scales RCUs up or down within the minimum and maximum range you set, based on three metrics:
CPU utilization
Memory pressure
Average active sessions (AAS)
When any metric reaches the scale-out threshold, the RCU count increases within minutes. When all three metrics drop below the scale-in threshold, the RCU count decreases within minutes.
Impact of changes
Changes to the RCU scaling range take effect in about one minute. The RCU count may change immediately depending on current usage.
Modifying the maximum RCU value
| Condition | Effect |
|---|---|
| Current RCU count < new maximum | RCU count stays the same |
| Current RCU count > new maximum | RCU count drops immediately to the new maximum |
| Current maximum is insufficient (instance is capacity-constrained) | RCU count increases immediately to the new maximum |
Example: A traffic spike occurs and the current maximum of 6 RCUs is insufficient. You raise it to 8. The RCU count increases to 8 as soon as the change takes effect.
Modifying the minimum RCU value
| Condition | Effect |
|---|---|
| Current RCU count > new minimum | RCU count stays the same |
| Current RCU count < new minimum | RCU count increases immediately to the new minimum |
Billing
Changing the RCU scaling range is free. RCU fees are calculated based on actual usage.
Change the RCU scaling range
Prerequisites
Before you begin, ensure that you have:
An RDS SQL Server Serverless instance
Sufficient permissions to modify instance configurations
Choose minimum and maximum values
RCU values must be integers in the range of 2–16.
| Parameter | Valid range | Guidance |
|---|---|---|
| Minimum RCU | 2–16 | Set the minimum value to prevent performance jitter during traffic spikes. A higher minimum reduces scale-out latency but increases baseline cost. |
| Maximum RCU | 2–16 | Caps resource usage and cost. Setting it too low risks throttling under unexpected load. Proceed with caution when lowering this value as it may affect instance performance. |
The minimum value must be less than or equal to the maximum value.
Steps
Go to the RDS Instances page. In the top navigation bar, select a region. Then click the ID of the target instance.
On the Basic Information page, find the Configuration Information section and click Adjust Elastic Settings.
In the dialog box, set the Minimum and Maximum values for Resource Scaling Range (RCU).
Click OK.
The new RCU scaling range takes effect within about one minute.
What's next
To increase storage capacity, see Increase storage space.
To reduce costs when the instance is idle, pause it. See Manually pause or start an instance and Billing for different instance statuses.
To release an instance you no longer need, see Release an instance.
RCU scaling typically completes in seconds. In rare cases, cross-machine scaling may take 3–5 minutes. To maintain stability during specific periods, schedule RCU configuration changes in advance.
To change the RCU scaling range using the API, see ModifyDBInstanceSpec.