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    Data Transmission Service:Track data changes from a PolarDB for PostgreSQL cluster

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    Data Transmission Service:Track data changes from a PolarDB for PostgreSQL cluster

    Last Updated:Mar 13, 2025

    This topic describes how to create a change tracking task to track data changes from a PolarDB for PostgreSQL cluster by using Data Transmission Service (DTS).

    Prerequisites

    • The source PolarDB for PostgreSQL cluster is created. For more information, see Create a cluster.

    • If the ApsaraDB RDS for MySQL instance is of the classic network type, an internal endpoint is configured for the ApsaraDB RDS for MySQL instance.

    Usage notes

    CategoryDescription
    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.

    • 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 value of the wal_level parameter must be set to logical. This setting ensures that logical encoding is supported in WAL. For more information, see Specify cluster parameters.
      Note The WAL logs of the source database must be stored for more than 24 hours. Otherwise, DTS may fail to obtain the WAL logs and the task may fail. In exceptional circumstances, data inconsistency or loss may occur. Make sure that you set the retention period of WAL 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.

    • If the source instance is a read-only or temporary instance, make sure that the instance records transaction logs.

    Other limits
    • A single change tracking task can track data changes from only one database. To track data changes from multiple databases, you must create a change tracking task for each database.
    • To ensure that the latency of change tracking is accurate, DTS adds a heartbeat table to the source database. The name of the heartbeat table is dts_postgres_heartbeat.

    • 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 columns of the FLOAT data type to 38 digits and the precision for columns of the DOUBLE data type to 308 digits.

    Procedure

    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.
      Note
      • If you log on to the DMS console and click the Enter Simple Mode icon in the upper-right corner, you can move the pointer over the p483176 icon in the upper-left corner, and then choose All functions > DTS > Change Tracking. For more information, see Customize the layout and style of the DMS console.
      • You can also configure the settings by using the new DTS console.
    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, specify the source database instance and the consumer network type.
      Warning

      After you specify the source database instance, we recommend that you read the Limits that are displayed in the upper part of the page. Otherwise, the task may fail or the tracked data cannot be consumed.

      SectionParameterDescription
      NoneTask Name

      The name of the change tracking task. DTS automatically assigns a name to the task. 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 an existing database connection

      The instance to which the source database belongs. You can choose whether to use an existing instance based on your business requirements.

      • If you use an existing instance, DTS automatically applies the parameter settings of the source database.

      • If you do not use an existing instance, you must set parameters for the source database.

      Database TypeThe type of the source database. Select PolarDB for PostgreSQL.
      Access MethodThe service that is used to access the source database. Select Alibaba Cloud Instance.
      Instance RegionThe region in which the source PolarDB for PostgreSQL cluster resides.
      Replicate Data Across Alibaba Cloud AccountsSpecify whether data is replicated across multiple Alibaba Cloud Accounts. You can select only No.
      Instance IDThe ID of the PolarDB for PostgreSQL instance.
      Database NameThe name of the source database.
      Database AccountThe account of the source database. Enter the privileged account of the PolarDB for PostgreSQL database.
      Database Password

      The password that is used to access the database instance.

      Consumer Network TypeNetwork Type

      The value of the Network Type parameter is fixed to VPC. You must select a VPC and a vSwitch. For more information, see VPCs.

      Note

      • After a change tracking task is configured, 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 connected to 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 database instance is an Alibaba Cloud database instance, such as an ApsaraDB RDS for MySQL or ApsaraDB for MongoDB instance, DTS automatically adds the CIDR blocks of DTS servers in the corresponding region to the whitelist of the instance. If the source database instance is a self-managed database hosted on an ECS instance, DTS automatically adds the CIDR blocks of DTS servers in the corresponding region to the security group rules of the ECS instance. To allow DTS to access the database, you must also manually add the CIDR blocks of DTS servers in the corresponding region to the security settings of the database. If the source database instance is a self-managed database that is deployed in a data center or provided by a third-party cloud service provider, you must manually add the CIDR blocks of DTS servers in the corresponding region to the security settings of the database to allow DTS to access the database. For more information, see the CIDR blocks of DTS servers section of the Add the CIDR blocks of DTS servers topic.

      Warning

      If the public CIDR blocks of DTS servers are automatically or manually added to the whitelist of a database instance or to the security group rules of an ECS instance, security risks may arise. Therefore, before you use DTS to track data changes, 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 security group rules and forbidding unauthorized CIDR blocks, or connecting the database instance to DTS by using Express Connect, VPN Gateway, or Smart Access Gateway.

    5. Select the objects for the change tracking task and configure advanced settings.
      ParameterDescription
      Data Change Types

      The data change types that you want to track. You can select only Data Update. DTS tracks data updates of the objects that you select. Data updates include the INSERT, DELETE, and UPDATE operations.

      Source Objects

      Select one or more objects from the Source Objects section and click the 向右小箭头 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 incremental data of all objects, including new objects in the database.

      • If you select a table as the object, DTS tracks only incremental data of this table. In this case, if you want to track data changes of another table, you must add the table to the object list. For more information, see Modify the objects for change tracking.

    6. Click Next: Advanced Settings and configure advanced settings.
      ParameterDescription
      Monitoring and Alerting
      Specify whether to configure alerting for the change tracking task. If the task fails or the latency exceeds the specified threshold, the specified alert contacts can receive notifications. Valid values:
      • No: does not configure alerts.
      • Yes: configures alerts. In this case, you must also specify the alert threshold and alert contacts.
      Retry Time for Failed Connections
      The retry time range for failed connections. If the change tracking task fails, DTS immediately retries a connection within the time range. Valid values: 10 to 1440. Unit: minutes. Default value: 120. We recommend that you set the time range to more than 30 minutes. If DTS reconnects to the source instance within the specified time range, DTS resumes the change tracking task. Otherwise, the change tracking task fails.
      Note
      • If an instance serves as the source or destination database of multiple change tracking tasks, the shortest retry time range 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.
      Configure ETL
      Specify whether to configure the extract, transform, and load (ETL) feature. For more information about ETL, see What is ETL?. Valid values:

    7. Click Next: Save Task Settings and Precheck in the lower part of the page.

      You can move the pointer over Next: Save Task Settings and Precheck and click Preview OpenAPI parameters to view the parameter settings of the API operation that is called to configure the instance.

      Note

      • 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 View Details next to each failed item. After you troubleshoot the issues based on the error message, you can run a precheck again.

      • If an alert is generated for an item during the precheck, perform the following operations based on the scenario:

        • If an alert item cannot be ignored, click View Details next to the failed item and troubleshoot the issues. Then, run a precheck again.

        • If the alert item can be ignored, click Confirm Alert Details. In the View Details dialog box, click Ignore. In the message that appears, click OK. Then, click Precheck Again to run a precheck again. If you ignore the alert item, data inconsistency may occur and your business may be exposed to potential risks.

    8. Wait until Success Rate becomes 100%. Then, click Next: Purchase Instance.

    9. On the Purchase Instance page, specify the billing method of the change tracking instance. The following table describes the parameters.
      ParameterDescription
      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.
      • 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 the pay-as-you-go instance to reduce costs.
      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. You can enable auto-renewal based on your business requirements.

    10. Read and select the Data Transmission Service (Pay-as-you-go) Service Terms.

    11. 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: