You can use Data Transmission Service (DTS) to track data changes from self-managed PosgreSQL databases and ApsaraDB RDS for PostgreSQL instances. This topic describes how to create a change tracking task to track data changes from an ApsaraDB RDS for PostgreSQL instance.

Prerequisites

Limits

Category Description
Limits on the source database
  • The source tables must have PRIMARY KEY or UNIQUE constraints and all fields must be unique. Otherwise, some 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 task to track more than 500 tables, a request error occurs. In this case, we recommend that you split the tables to be tracked, configure multiple tasks to track the tables, or configure a change tracking task for the entire database.
  • The following requirements for write-ahead logging (WAL) logs must be met:
    • The value of the wal_level parameter must be set to logical.
    • 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 in accordance with the preceding requirements. Otherwise, the Service Level Agreement (SLA) of DTS does not ensure service reliability or performance.

  • A read-only instance or temporary instance cannot be used as the source instance for change tracking.
  • If you need to perform a primary/secondary switchover on the source ApsaraDB RDS for PostgreSQL instance, the Logical Replication Slot Failover feature must be enabled. This prevents logical subscriptions from being interrupted and ensures that your change tracking task can run as expected. For more information, see Logical Replication Slot Failover.
Other limits
  • You cannot track the schema updates of the source instance.
  • 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.
  • When DTS runs the change tracking task, DTS creates a replication slot for the source database. The replication slot is prefixed with dts_sync_. DTS automatically clears historical replication slots every 90 minutes to reduce storage usage.
    Note If the change tracking task is released or fails, DTS automatically clears the replication slot. If a primary/secondary switchover is performed on the source ApsaraDB RDS for PostgreSQL instance, you must log on to the secondary instance to clear the replication slot.
    Replication slot information
  • A single change tracking task can track data changes from only a single database. To track data changes from multiple databases, you must create a change tracking task for each database.
  • 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 data definition language (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.
Special cases When you track data changes from the source ApsaraDB RDS for PostgreSQL instance, do not change the endpoint or zone of the ApsaraDB RDS for PostgreSQL instance. Otherwise, the change tracking task fails.

Procedure

  1. Go to the Change Tracking page of the new DTS console.
  2. In the upper-left corner of the page, select the region where the change tracking instance resides.
    Select a region
  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 at the top of the page. This helps you create and run the change tracking task.
    Configure the source and destination databases
    Section Parameter Description
    N/A Task Name

    DTS automatically generates a task name. We recommend that you specify an informative name to identify the task. You do not need to use a unique task name.

    Source Database Select Template
    You can choose whether to use a database connection template.
    • If you use a connection template, DTS automatically applies the parameter settings of the source database.
      Note
      • You can modify the parameter settings of a connection template.
      • To edit the template name, you can click Edit Template Name at the bottom of the Source Database section.
      • The modified connection template will take 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 a connection template, you must set parameters for the source database.
    Database Type Select PostgreSQL.
    Access Method Select Alibaba Cloud Instance.
    Instance Region Select the region in which the ApsaraDB RDS for PostgreSQL instance resides.
    Instance ID Select the ID of the ApsaraDB RDS for PostgreSQL instance.
    Database Name Enter the name of the source database.
    Database Account Enter the privileged account of the ApsaraDB RDS for PostgreSQL instance. The account must be the owner of the database. For more information about how to create an account on an ApsaraDB RDS for PostgreSQL instance and grant permissions to this account, see Create an account on an ApsaraDB RDS for PostgreSQL instance and Create a database on an ApsaraDB RDS for PostgreSQL instance.
    Database Password

    Enter the password of the database account.

    Save as Template
    Consumer Network Type
    • Classic
    • VPC
    Select the network type of the change tracking instance.
    Note
    • If your change tracking client is deployed on a local server, you can select Classic or VPC.
    • If your change tracking client is deployed on an ECS instance, we recommend that you select the network of the ECS instance. For example, if the ECS instance is deployed in a VPC, select VPC as the network type and specify the VPC and vSwitch parameters.
    • If you track data changes over internal networks, the network latency is minimal.
    • Classic

      If you select Classic, no other configurations are required. For more information, see Classic network.

    • VPC

      If you select VPC, you must specify the VPC and vSwitch parameters. For more information, see VPCs.

    Notice After a change tracking task is configured, you cannot change the network type. Data changes are tracked and consumed over the specified type of network.
  4. In the lower part of the page, click Test Connectivity and Proceed.
  5. Select objects for the task and configure advanced settings.
    • Basic Settings
      Parameter Description
      Data Change Types

      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 Rightwards arrow icon to move 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
      Parameter Description
      Set Alerts
      Specify 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.
      • Select No if you do not want to set alerts.
      • Select Yes to set alerts. In this case, you must also set the alert threshold and alert contacts.
      Retry Time for Failed Connections
      Specify 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.
      Note
      • If multiple DTS instances have the same source or destination database, the lowest value takes effect. For example, the retry time is set to 30 minutes for Instance A and 60 minutes for Instance B, DTS retries failed connections at an interval of 30 minutes.
      • When DTS retries a connection, you are charged for the DTS instance. We recommend that you specify the retry time based on your business needs. 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.
    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, you can click the Info icon icon next to each failed item to view details.
      • You can troubleshoot the issues based on the causes and run a precheck again.
      • If you do not need to troubleshoot the issues, you can 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.
    Parameter Description
    Billing Method
    • Subscription: You can pay for your subscription when you create an instance. We recommend that you select the subscription billing method for long-term use because it is more cost-effective than the pay-as-you-go billing method. You can save more costs with longer subscription periods.
    • Pay-as-you-go: A pay-as-you-go instance is billed on an hourly basis. We recommend that you select the pay-as-you-go billing method for short-term use. If you no longer require your 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, you can select only USD 120 per month for configuration fee (no data traffic fee) as the billing type of the change tracking instance.

    Subscription Length
    If you select the subscription billing method, set the subscription length and the number of instances that you want to create. The subscription length can be one to nine months or one to three years.
    Note This parameter is available only if you select the subscription billing method.
    Note When a client accesses the change tracking instance over the Internet, DTS charges Internet traffic fee.
  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. Create and manage consumer groups. For more information, see Create consumer groups.
  2. Use one of the following methods to consume the tracked data: