PolarDB for MySQL clusters with subscription or pay-as-you-go billing can add serverless auto-scaling to dynamically adjust each node's PolarDB Capacity Unit (PCU) allocation based on workload. After enablement, each node scales within the range of (defined specifications + minimum PCU) to (defined specifications + maximum PCU), retaining its base capacity while gaining elastic scaling.
How it works
Serverless on a defined-spec cluster is an additive model: the system layers serverless scaling on top of existing provisioned resources.
For example, if a node has 4 cores of defined specifications and you set the PCU range to 2-8:
Minimum effective capacity: 4 cores + 2 PCU (approximately 2 cores and 4 GB memory) = approximately 6 cores
Maximum effective capacity: 4 cores + 8 PCU (approximately 8 cores and 16 GB memory) = approximately 12 cores
Component architecture
| Component | Behavior |
|---|---|
| PolarProxy | Uses a serverless architecture independent of compute nodes. Resources scale automatically in units of 0.5 PCU. No manual configuration is required. |
| Compute nodes | The primary node and read-only nodes adopt serverless scaling. Resources scale in units of 0.5 PCU based on workload. The system monitors PCU usage every second. |
| Storage | Uses pay-as-you-go billing. Capacity grows automatically as data increases. You pay only for the storage space used. Check Database Storage Usage on the Basic Information page. For details, see View the database storage usage. |
When serverless is enabled for a cluster with defined specifications, the maximum number of connections is 100,000. Scalable IOPS is proportional to the configured upper limit for a single serverless node. The No-activity Suspension feature is not supported.
Prerequisites
Before you begin, make sure that your cluster meets the following requirements:
Minor engine version:
MySQL 5.7: 5.7.1.0.29 or later
MySQL 8.0.1: 8.0.1.1.30.1 or later
MySQL 8.0.2: 8.0.2.2.19 or later
NoteMySQL 5.6 is not supported.
Database proxy (Proxy) version: 2.4.30 or later
CPU architecture: X86 only. Yitian ARM is not supported.
Limitations
| Limitation | Details |
|---|---|
| Single-node clusters without PolarProxy | Serverless cannot be enabled for an existing single-node cluster without PolarProxy. Add read-only nodes first. See Add a node. You can enable serverless for a new single-node cluster that meets the version requirements. |
| Manual storage scaling | Manually scale up or scale down the storage capacity is not supported for Enterprise Edition clusters. |
| PCU scaling caps (dedicated specifications) | Not supported for nodes with more than 32 CPU cores. |
| PCU scaling caps (general-purpose specifications) | Not supported for nodes with more than 16 CPU cores. |
| Mutual exclusion with auto scaling | If serverless is enabled, auto scaling for non-serverless clusters cannot be enabled, and vice versa. |
| X-Engine support | Available for MySQL 8.0.1 revision 8.0.1.1.41 or later and MySQL 8.0.2 revision 8.0.2.2.23 or later. |
| Global Database Network (GDN) | Supported with restrictions: automatic start and stop cannot be enabled on all serverless clusters in a GDN. Each serverless cluster in the GDN must have at least one read-only node if the version is MySQL 8.0.1 (revision 8.0.1.1.42 or later) or MySQL 8.0.2 (revision 8.0.2.2.23 or later). |
| Read-only column store nodes | Can be added to the cluster and configured after serverless is enabled. |
Enable serverless
The cluster may be migrated to an idle host due to resource shortage during enablement. Enable serverless during off-peak hours.
Primary endpoint: A disconnection of 5-10 seconds occurs during migration.
Cluster endpoint: No disconnection occurs. Use a cluster endpoint and make sure that failover with hot replica is active. See Connecting to a PolarDB cluster and Failover with hot replica.
Log on to the PolarDB console.
In the left-side navigation pane, click Clusters.
In the upper-left corner, select the region where the cluster is deployed.
Click the cluster ID to open the Basic Information page.
In the Database Nodes section, click Enable Serverless.
In the Enable Serverless dialog box, configure the following parameters, and then click OK.
Single-node resource range
| Parameter | Description | Valid values |
|---|---|---|
| Maximum Resources for Single Node | Maximum PCU that can be added to each node beyond its defined specifications. | 0-16 PCU |
| Minimum Resources for Single Node | Minimum PCU that can be added to each node beyond its defined specifications. Must be less than or equal to the maximum. | 0-16 PCU |
One PCU is approximately equal to 1 CPU core and 2 GB of memory. Resources scale in units of 0.5 PCU. The values do not include the defined specifications of the cluster. The effective range for each node is (defined specifications + minimum) to (defined specifications + maximum).
Example: Set the minimum to 2 PCU and the maximum to 8 PCU. Each node starts with defined specifications plus 2 PCU (approximately 2 cores, 4 GB). Under load, each node can scale up to defined specifications plus 8 PCU (approximately 8 cores, 16 GB).
Automatically added read-only nodes use a default scaling range of 1-32 PCU. This range does not need to be specified.
Read-only node range
| Parameter | Description | Valid values |
|---|---|---|
| Maximum Read-only Nodes | Maximum number of read-only nodes that can be automatically added. | 0-15 |
| Minimum Read-only Nodes | Minimum number of read-only nodes that can be automatically added. Cannot exceed the maximum. | 0-15 |
These values do not include the original read-only nodes already in the cluster.
Example: Set the minimum to 1 and the maximum to 2. One read-only node is added immediately. Under load, the system can add up to two read-only nodes on top of the original count.
Read-only column store nodes
| Parameter | Description | Valid values |
|---|---|---|
| Read-only Column Storage Nodes | Number of read-only column store nodes to add. | 0-15 |
This value does not include the original read-only column store nodes. This parameter appears only when the cluster already has read-only column store nodes.
A cluster supports a maximum of 15 read-only nodes in total. Make sure the sum of original read-only nodes, automatically added read-only nodes, and read-only column store nodes does not exceed 15.
Verify enablement
After you click OK, the serverless feature takes effect on the cluster.
On the Basic Information page, confirm that the Database Nodes section displays Serverless: Enabled along with the Serverless Configuration and Disable Serverless buttons.
Go to Performance Monitoring and check the Serverless Monitoring Metrics section. This section displays PCU, CPU usage, and memory usage charts for each node. The node specifications show the format (defined specifications + PCU range), for example, "4 Cores, 8 GB of Local Memory + (2~8) PCU".
Usage notes
Maximum connections and IOPS are proportional to the Maximum Resources for Single Node value.
Dynamic parameter adjustment: After enablement, the values of
innodb_buffer_pool_size,loose_thread_pool_size, andtable_open_cacheare dynamically adjusted to match the current PCU allocation. Disabling serverless restores the original values.
Billing
The total cost for a serverless-enabled cluster with defined specifications consists of two parts:
| Fee component | Description |
|---|---|
| Defined specifications fees | Base cost for the provisioned cluster resources |
| Serverless fees | Cost for the additional serverless PCU consumption |
Next steps
API reference
| API | Description |
|---|---|
| EnableDBClusterServerless | Enable serverless for a cluster with defined specifications |
| DescribeDBClusterServerlessConf | Query the serverless configuration of a cluster |