Data Transmission Service:Create a PolarDB for MySQL change tracking task

Source database requirements

• Tables must have PRIMARY KEY or UNIQUE constraints with no duplicate fields. Without these, some tracked changes may be duplicated.

• A single change tracking task supports up to 500 tables. Exceeding this limit causes a request error. To track more than 500 tables, split them across multiple tasks or track the entire database instead.

• Binary logging must be enabled, and loose_polar_log_bin must be set to on. If not configured correctly, the precheck fails and the task cannot start.

• DTS requires binary logs to be retained for more than 24 hours. Shorter retention periods can cause the task to fail and, in extreme cases, data inconsistency or loss. Issues caused by insufficient binary log retention are not covered by the DTS Service-Level Agreement (SLA).

• Read-only and temporary instances must have transaction logs enabled.

Other limitations

• For FLOAT and DOUBLE columns, DTS uses ROUND(COLUMN, PRECISION) to retrieve values. If no precision is specified, DTS defaults to 38 digits for FLOAT and 308 digits for DOUBLE. Verify that these defaults meet your requirements before starting the task.

• DTS does not track DDL operations performed using pt-online-schema-change. This can cause schema conflicts when the change tracking client writes consumed data to destination tables.

• Rows larger than 16 MB cannot be consumed. Attempting to do so may cause an out of memory (OOM) error on the change tracking client.

• If a DTS instance fails, the DTS helpdesk attempts recovery within 8 hours. Recovery operations may include restarting the instance or adjusting parameters — only DTS instance parameters are modified, not database parameters.

Step 1: Open the Change Tracking Tasks page

Use one of the following methods to navigate to the Change Tracking Tasks page.

Step 2: Configure the source database

1. On the Change Tracking Tasks page, click Create Task.

2. In the Source Database and Consumer Network Type sections, configure the following parameters.

   Warning

   After selecting the source database instance, read the Limits displayed at the top of the page. Skipping this step may cause the task to fail or prevent you from consuming tracked data.

   Parameter	Description
   Task Name	A descriptive name for the change tracking task. DTS assigns a name automatically, but a meaningful name makes the task easier to identify. Names don't need to be unique.
   Select Existing Connection	If the database is already registered with DTS, select it from the list — DTS fills in the connection details automatically. Otherwise, enter the database information manually.
   Database Type	Select PolarDB for MySQL.
   Access Method	Select Alibaba Cloud Instance.
   Instance Region	Select the region where the PolarDB for MySQL cluster resides.
   Replicate Data Across Alibaba Cloud Accounts	Select No for same-account tracking. To track data across Alibaba Cloud accounts, select Yesalert notification settings and provide the Alibaba Cloud Account and RAM Role Name. You must also configure Resource Access Management (RAM) authorization for the account used to set up the DTS task. See Configure RAM authorization for cross-account DTS tasks.
   PolarDB Cluster ID	Select the PolarDB for MySQL cluster ID.
   Database Account	Enter the Read-only Account for the PolarDB for MySQL cluster, or a custom account with the REPLICATION CLIENT, REPLICATION SLAVE, SHOW VIEW, and SELECT permissions.
   Database Password	The password for the database account.
   Encryption	Select an encryption method as needed. For Secure Sockets Layer (SSL) encryption, see Set SSL encryption.
   Network Type	Fixed to VPC. Select the VPC and vSwitch for the change tracking instance. If the change tracking client is deployed in a VPC, select the same VPC and vSwitch as the client to minimize network latency. This setting cannot be changed after the task is configured.

3. Click Test Connectivity and Proceed.

   DTS server IP addresses must be added to the allowlist of your source database. See Add DTS server IP addresses to a whitelist.

Step 3: Select objects to track

On the Configure Objects page, configure the following settings:

Click Next: Advanced Settings.

Step 4: Configure advanced settings

Step 5: Run the precheck and purchase the instance

1. Click Next: Save Task Settings and Precheck. To preview the API parameters for this task configuration, hover over Next: Save Task Settings and Precheck and click Preview OpenAPI parameters before proceeding.

   - DTS runs a precheck before the task starts. The task can only start after the precheck passes. - If any item fails, click View Details next to the failed item and fix the issue. Then rerun the precheck. - If an alert is generated for an item: fix and recheck items that cannot be ignored; for ignorable alerts, click Confirm Alert Details, then Ignore, confirm, and click Precheck Again. Ignoring alerts may cause data inconsistency.

2. Wait until Success Rate reaches 100%, then click Next: Purchase Instance.

3. On the Purchase page, configure the billing method.

   Parameter	Description
   Billing method	Subscription — pay upfront, lower cost for long-term use. Duration options: 1–9 months, or 1, 2, 3, or 5 years. Pay-as-you-go — billed hourly, suitable for short-term use. Release the instance when no longer needed to stop charges.
   Resource Group Settings	The resource group for the instance. Defaults to default resource group. See What is Resource Management?
   Subscription Duration	Available for the Subscription billing method only. Select the subscription period and number of instances.

4. Read and accept the Data Transmission Service (Pay-as-you-go) Service Terms.

5. Click Buy and Start. The task appears in the task list where you can monitor its progress.