When analytical queries share compute resources with transactional workloads on the same primary instance, heavy Clustered Columnar Index (CCI) queries can degrade OLTP performance. A read-only columnar instance offloads CCI query workloads to dedicated compute nodes, giving your primary instance consistent headroom for transactional traffic.
How it works
PolarDB-X CCI uses a component-based read/write splitting architecture with two node types:
Columnar nodes — write row-oriented storage data.
Compute nodes — read column-oriented data.
A read-only columnar instance is a separate set of compute nodes dedicated to CCI queries. It is physically isolated from the primary instance's CCI query traces, so analytical and transactional workloads no longer compete for the same resources.
Constraints
The read-only columnar instance must be in the same region as the primary instance, but can be in a different zone.
The instance cannot exist independently. It is bound to the primary instance: databases created or deleted on the primary instance are automatically replicated to or removed from all associated read-only instances.
The instance can only access tables that contain CCIs. Queries against tables without CCIs return a query-limit error.
Add a read-only columnar instance
Prerequisites
Before you begin, ensure that you have:
An Alibaba Cloud account balance of at least USD 100 if you plan to use Pay-as-you-go billing
Procedure
Log on to the PolarDB-X console.
In the top menu bar, select the region where your primary instance is deployed.
On the Instance List page, click the PolarDB-X 2.0 tab.
Open the configuration dialog using either of the following entry points:
In the Actions column for your instance, click Read-only Columnar Instance.
Click the instance ID. On the instance details page, go to the Read-only Columnar Instance section and click Add Read-only Columnar Instance.
Configure the parameters in the dialog box.
Billing and duration
Parameter Description Billing Method Subscription: pay before use; lower unit price; suited for long-term production use. Pay-as-you-go: billed by actual usage; suited for testing. Duration Subscription duration. Applies only when Billing Method is set to Subscription. Quantity Number of read-only columnar instances to purchase. Network
Parameter Description Region Automatically set to match the primary instance's region. Read-only and primary instances must be in the same region. Zone Zone for the read-only columnar instance. Can differ from the primary instance's zone. Network Type Fixed to VPC. VPC Name of the Virtual Private Cloud (VPC). vSwitch Name of the vSwitch. Instance specifications
Parameter Description MySQL Version Fixed to 5.7. Instance Model Fixed to Custom Model. Instance Type Standard or Dedicated. Compute Node Specifications CPU cores and memory per compute node. Total capacity = Compute Node Specifications x Compute Nodes. Compute Nodes Number of compute nodes. Default: 2. Read-only columnar instances contain only compute nodes — no row store nodes. Storage Type Fixed to Local SSD Disk. Storage Cost No storage charges apply to columnar compute nodes. No capacity selection is required. Read the terms of service, select Terms of Service, and click Buy Now.
On the Purchase page, confirm the order and payment method, then click Purchase.
After payment, the instance takes approximately 3 to 5 minutes to create. Once ready, it appears on the Instance List page in the PolarDB-X console.