RDS Capacity Units (RCUs) are a representation of the performance of a serverless ApsaraDB RDS for SQL Server instance. The system automatically adjusts the RCUs of the serverless RDS instance within the range that you specified based on workloads. You can also manually change the scaling range of RCUs.
Scenarios
Traffic spikes are expected to occur and may affect the load and cause performance jitters. In this case, you can increase the minimum number of RCUs to prevent this issue.
If you want to reduce costs, you can reduce the maximum number of RCUs. This operation may affect the performance of the serverless RDS instance. Proceed with caution.
Feature description
The scaling of RCUs for a serverless RDS instance depends on the CPU utilization, memory usage, and average active sessions (AAS) metrics of the serverless RDS instance. If one of the prceding metrics reaches the threshold for a scale-up, the system automatically scales up the number of RCUs within 5 to 10 seconds. If one of the preceding metrics reaches the threshold for a scale-down, the system automatically scales down the number of RCUs within 15 to 20 seconds.
Impacts
The RCU scaling for a serverless RDS instance takes effect within approximately 1 minute.
The scaling of RCUs causes the following impacts:
Change the maximum number of RCUs
If the current number of RCUs is smaller than the new maximum number of RCUs, the number of RCUs remains unchanged.
If the current number of RCUs is greater than the new maximum number of RCUs, the number of RCUs is immediately decreased to the new maximum number after the configuration takes effect.
If the current maximum number of RCUs does not meet your business requirements, the number of RCUs is immediately increased to the new maximum number after the configuration takes effect.
For example, a traffic spike occurs, the current maximum number of RCUs is 6 and cannot meet your business requirements, and the new maximum number of RCUs is 8. The system immediately increases the number of RCUs to 8 after the configuration takes effect.
Change the minimum number of RCUs
If the current number of RCUs is greater than the new minimum number of RCUs, the number of RCUs remains unchanged.
If the current number of RCUs is smaller than the new minimum number of RCUs, the number of RCUs is immediately increased to the new minimum number after the configuration takes effect.
Billing rules
You are not charged for changing the number of RCUs. The fee for a serverless RDS instance depends only on the actual usage of RCUs and storage resources. For more information, see Pricing of a serverless ApsaraDB RDS for SQL Server instance.