You can use Data Transmission Service (DTS) to track data changes in real time. You can use the change tracking feature in the following scenarios: lightweight cache updates, business decoupling, asynchronous data processing, and synchronization of extract, transform, and load (ETL) operations. This topic describes how to create a change tracking task to track data changes from a PolarDB for MySQL cluster.


Usage notes

Limits on the source database
  • The source tables must have PRIMARY KEY or UNIQUE constraints and all fields must be unique. Otherwise, part of the tracked data changes may be duplicate.
  • If you select tables as the objects to be tracked, up to 500 tables can be tracked in a single change tracking task. If you run a change tracking task to track more than 500 tables, a request error occurs. In this case, we recommend that you configure multiple tasks to track the tables in batches or configure a change tracking task for the entire database.
  • The following requirements for binary logs must be met:
    • The binary logging feature must be enabled. The value of the loose_polar_log_bin parameter must be set to on. Otherwise, error messages are returned during precheck and the change tracking task cannot be started.

    • The binary logs of the source database are stored for more than 24 hours. Otherwise, DTS may fail to obtain the binary logs and the task may fail. In exceptional circumstances, data inconsistency or loss may occur. Make sure that you set the retention period of binary logs based on the preceding requirements. Otherwise, the service reliability and performance stated in the Service Level Agreement (SLA) of DTS may not be guaranteed.
  • A read-only instance or temporary instance cannot be used as the source instance for change tracking.
Other limits
  • You must make sure that the precision settings for columns of the FLOAT or DOUBLE data type meet your business requirements. DTS uses the ROUND(COLUMN,PRECISION) function to retrieve values from columns of the FLOAT or DOUBLE data type. If you do not specify a precision, DTS sets the precision for the FLOAT data type to 38 digits and the precision for the DOUBLE data type to 308 digits.
  • DTS does not track the DDL operations that are performed by using gh-ost or pt-online-schema-change. Therefore, the change tracking client may fail to write the consumed data to the destination tables due to schema conflicts.


  1. Go to the Change Tracking Tasks page.
    1. Log on to the Data Management (DMS) console.
    2. In the top navigation bar, click DTS.
    3. In the left-side navigation pane, choose DTS (DTS) > Change Tracking.
  2. To the right of Change Tracking Tasks, select the region in which you want to create the change tracking task.
    Note If you use the new DTS console, you must select the region from the drop-down list to the right of Workbench on the Change Tracking Tasks page of the DTS console.
  3. Click Create Task. On the page that appears, configure the source database and the consumer network type.
    Warning After you select the source instance, we recommend that you read the limits displayed in the upper part of the page. This helps you create and run the change tracking task.
    NoneTask Name

    The task name that DTS automatically generates. We recommend that you specify a descriptive name that makes it easy to identify the task. You do not need to use a unique task name.

    Source DatabaseSelect Instance
    The instance that you want to use. You can choose whether to select an existing instance based on your business requirements.
    • If you use an existing instance, DTS automatically applies the parameter settings of the instance.
      • To modify the connection settings of a template, you can edit the template when you configure the Select Instance parameter in the Source Database section.
      • To edit the template name, you can click Edit Template in the lower part of the Source Database section.
      • The modified connection template takes effect the next time you select the connection template. The database instance that you have configured by using the template is not affected.
    • If you do not use an existing instance, you must configure the following parameters.
    Database TypeThe type of the source database. Select PolarDB for MySQL.
    Access MethodThe service that is used to access the source database. Select Alibaba Cloud Instance.
    Instance RegionThe region in which the source PolarDB for MySQL cluster resides.
    PolarDB Cluster IDThe ID of the PolarDB for MySQL cluster.
    Database AccountThe account of the source database. Enter a database account that has read-only permissions on the PolarDB for MySQL cluster, or a custom account that has the REPLICATION CLIENT, REPLICATION SLAVE, SHOW VIEW, and SELECT permissions.
    Database Password

    The password of the database account.


    Select Non-encrypted or SSL-encrypted based on your business requirements. If you want to select SSL-encrypted, you must enable SSL encryption for the source instance before you configure the change tracking task. For more information, see Configure SSL encryption for an ApsaraDB RDS for MySQL instance.

    Consumer Network TypeNetwork Type
    The Network Type parameter is set to VPC. You must select a VPC and a vSwitch. For more information, see VPCs.
    • After the task is created, you cannot change the settings in the Consumer Network Type section.
    • If your change tracking client is deployed in a VPC, we recommend that you select the same VPC and vSwitch as the client.
    • If you track data changes over internal networks, the network latency is minimal.
  4. In the lower part of the page, click Test Connectivity and Proceed.
    • If the source or destination database instance is an Alibaba Cloud database instance, such as an ApsaraDB RDS for MySQL or ApsaraDB for MongoDB instance, or is a self-managed database hosted on ECS, DTS automatically adds the CIDR blocks of DTS servers to the whitelist of the database instance or ECS security group rules. For more information, see Add the CIDR blocks of DTS servers to the security settings of on-premises databases. If the source or destination database is a self-managed database on data centers or is from other cloud service providers, you must manually add the CIDR blocks of DTS servers to allow DTS to access the database.
    • If the CIDR blocks of DTS servers are automatically or manually added to the whitelist of the database, Alibaba Cloud database instance, or ECS security group rules, security risks may arise. Therefore, before you use DTS to migrate data, you must understand and acknowledge the potential risks and take preventive measures, including but not limited to the following measures: enhancing the security of your username and password, limiting the ports that are exposed, authenticating API calls, regularly checking the whitelist or ECS security group rules and forbidding unauthorized CIDR blocks, or connecting the database to DTS by using Express Connect, VPN Gateway, or Smart Access Gateway.
    • After the DTS task is complete or released, we recommend that you manually detect and remove the added CIDR blocks from the whitelist of the database, Alibaba Cloud database instance, or ECS security group rules.
  5. Select objects for the task and configure advanced settings.
    • Basic Settings
      Data Change Types
      • Data Update

        DTS tracks data updates of the selected objects, including the INSERT, DELETE, and UPDATE operations.

      • Schema Updates

        DTS tracks the create, delete, and modify operations that are performed on all object schemas of the source instance. You must use the change tracking client to filter the required data.

      Source Objects
      Select one or more objects from the Source Objects section and click the Rightwards arrow icon to add the objects to the Selected Objects section.
      Note You can select tables or databases as the objects for change tracking.
      • If you select a database as the object, DTS tracks data changes of all objects, including new objects in the database.
      • If you select a table as the object, DTS tracks only data changes of this table. In this case, if you want to track data changes of another table, you must add the table to the selected objects. For more information, see Modify the objects for change tracking.
    • Advanced Settings
      Set Alerts
      Select whether to set alerts for the change tracking task. If the task fails or the latency exceeds the threshold, the alert contacts will receive notifications. Valid values:
      • No: does not set alerts.
      • Yes: sets alerts. In this case, you must also set the alert threshold and alert contacts.
      Retry Time for Failed Connections
      The retry time for failed connections. Valid values: 10 to 1440. Unit: minutes. Default value: 120. We recommend that you set the retry time to more than 30 minutes. If DTS reconnects to the source and destination databases within the specified time, DTS resumes the change tracking task. Otherwise, the change tracking task fails.
      • If an instance serves as the source database of multiple change tracking tasks, the less value of this parameter that is set for the instance takes precedence.
      • When DTS retries a connection, you are charged for the DTS instance. We recommend that you specify the retry time range based on your business requirements. You can also release the DTS instance at your earliest opportunity after the source and destination instances are released.
  6. Click Next: Save Task Settings and Precheck in the lower part of the page.
    • Before you can start the change tracking task, DTS performs a precheck. You can start the change tracking task only after the task passes the precheck.
    • If the task fails to pass the precheck, click the Info icon icon next to each failed item to view details.
      • After you troubleshoot the issues based on the causes, run a precheck again.
      • If you do not need to troubleshoot the issues, ignore failed items and run a precheck again.
  7. Wait until the Success Rate becomes 100%. Then, click Next: Purchase Instance.
  8. On the Purchase Instance page, specify the billing method of the change tracking instance. The following table describes the parameters.
    Billing method
    • Subscription: You pay for the instance when you create an instance. The subscription billing method is more cost-effective than the pay-as-you-go billing method for long-term use. You are offered lower prices for longer subscription periods.
    • Pay-as-you-go: A pay-as-you-go instance is billed on an hourly basis. The pay-as-you-go billing method is suitable for short-term use. If you no longer require a pay-as-you-go instance, you can release it to reduce costs.
    Billing Type of Change Tracking Instance

    If you select the subscription billing method, Billing Type for Change Tracking Instance is set to USD 120 per month for configuration fee (no data traffic fee).

    Subscription Length
    If you select the subscription billing method, set the subscription duration and the number of instances that you want to create. The subscription duration can be one to nine months or one to three years.
    Note This parameter is available only if you select the subscription billing method.
  9. Read and select Data Transmission Service (Pay-as-you-go) Service Terms.
  10. Click Buy and Start to start the change tracking task. You can view the progress of the task in the task list.

What to do next

When the change tracking task is running, you can create consumer groups based on the downstream client to consume the tracked data.
  1. For more information about how to create and manage consumer groups, see Create consumer groups.
  2. Use one of the following methods to consume the tracked data: