Why Is the CPU Elastic Scale-Out Feature Not Visible in the Console?
The CPU elastic scale-out feature has the following requirements for instances. If these requirements are not met, the console will not display the entry for this feature.
The instance must run MongoDB version 4.0 or later.
The instance must not be of Cloud Disk Edition.
The original number of CPU cores for an instance cannot exceed 32.
Which Instances Do Not Support CPU Elastic Scale-Out?
The following instances cannot be enabled at this time:
Instances running MongoDB versions earlier than 4.0.
Instances of Cloud Disk Edition.
Instances whose original number of CPU cores exceeds 32 (for example, a 48-core specification).
How Many CPU Cores Can Elastic Scale-Out Add?
The number of cores added in a single scale-up is MIN (the number of cores of the current smallest shard, 24 cores):
For replica set instances, the number of CPU cores can be increased by a maximum of 24 based on the original number.
For sharded cluster instances, the scale-up limit for a single shard is the smaller value between the smallest number of cores among all shards and 24 cores.
Why Does IOPS Remain Unchanged After Scale-Out?
TencentDB for MongoDB currently does not impose granular restrictions on IOPS. Therefore, IOPS does not change with the number of CPU cores. CPU elastic scale-out only adjusts the number of CPU cores and does not include additional IOPS resources.
How Is CPU Elastic Scale-Out Billed?
CPU elastic scale-out is billed in pay-as-you-go mode. The fee = (unit price per core × number of additional CPU cores) × scale-up duration (minutes) / 60. For custom scale-ups, fees are charged continuously until you manually disable them, after which charging stops. For details, see Billing Description. Why Are Fees Charged Continuously After Custom Scale-Out Is Enabled?
After custom scale-out is enabled, the scale-out takes effect immediately and remains active, with continuous billing. It does not automatically scale back before you manually disable it. When your workload no longer requires additional resources, manually disable scale-up promptly to stop billing.
Why Did CPU Elastic Scale-Out Fail to Enable?
Possible causes include:
Insufficient balance in your Tencent Cloud account.
Insufficient CPU resources on the underlying machine (extremely low probability).
Ensure your account has sufficient balance and then retry. If the operation still fails, you can submit a ticket for consultation.
Why Does Elastic Scale-Out Automatically Disable After Being Enabled for a Period?
After you manually adjust the specifications of a Mongod node, the CPU elastic scale-out feature is automatically disabled. Monitor the CPU usage of your workload after the specification change. If you need to continue using elastic scale-out, manually re-enable it after the change.
In addition, during the operation of scaling Mongod nodes or changing Mongos, elastic scale-out is temporarily disabled and will not be triggered. It automatically recovers after the operation is completed.
What to Do If Scale-Out Fails for Some Shards in a Sharded Cluster Instance?
Elastic scale-out is performed on sharded cluster instances as a whole. This allows for scenarios where scale-out succeeds for some shards but fails for others. When partial success occurs, the task execution status is displayed as Scale-out Partially Successful, and alarms are triggered by the backend for the unsuccessful shards. You can view the execution status of each task in Scale-up History. Does Enabling Elastic Scale-Put Affect Operations Such as Backup and Clone?
No impact. The CPU addition process triggered by elastic scale-out does not lock with non-essential locking processes such as cloning, backup, and full-instance rollback, allowing them to proceed concurrently. Furthermore, elastic scale-out does not block vertical or horizontal scaling. When your workload needs to handle prolonged peak periods, you can interrupt the elastic scale-up process by manually upgrading the configuration.
How to Determine Whether Scale-Out Has Taken Effect
Check the number of CPU cores at the instance specification section on the instance details page. If the actual number of cores is displayed in addition to the original number (for example, 4 (8) cores), it indicates that scale-up to 8 cores has been performed. If only the original number of cores is displayed, it indicates that scale-up has not been triggered.