Track data changes from an ApsaraDB RDS for PostgreSQL instance - Data Transmission Service

You can use Data Transmission Service (DTS) to track data changes from self-managed PostgreSQL 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

The source ApsaraDB RDS for PostgreSQL instance is created. For more information, see Create an ApsaraDB RDS for PostgreSQL instance.
The wal_level parameter is set to logical for the source ApsaraDB RDS for PostgreSQL instance. For more information, see Modify the parameters of an ApsaraDB RDS for PostgreSQL instance.
The source ApsaraDB RDS for PostgreSQL instance runs PostgreSQL 9.4, 10, 11, 12, 13, 14, or 15.
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

Category	Description
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 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 change tracking 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. 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	If you need to track the schema updates of the source ApsaraDB RDS for PostgreSQL instance, create a trigger and a function in the source database to obtain DDL information of the source database. For more information, see Use triggers and functions to implement incremental DDL migration for PostgreSQL databases. 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 database to clear the replication slot. 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. 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.
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

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 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.
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.

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.

Section	Parameter	Description
None	Task 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 Database	Select 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 Type	The type of the source database. Select PostgreSQL.
	Access Method	The service that is used to access the source database. Select Alibaba Cloud Instance.
	Instance Region	The region in which the source ApsaraDB RDS for PostgreSQL instance resides.
	Instance ID	The ID of the source ApsaraDB RDS for PostgreSQL instance.
	Database Name	The name of the source database.
	Database Account	The account of the source database. 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 and Create a database.
	Database Password	The password that is used to access the database instance.
Consumer Network Type	Network 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.

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.

Configure the objects for change tracking and advanced settings.

Basic Settings

Parameter	Description
Data Change Types	Data Update DTS tracks data updates of the selected objects, including the INSERT, DELETE, and UPDATE operations. Schema Update 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 data to be tracked. Note If you select Schema Update, you need to create a trigger and a function in the source database to obtain DDL information of the source database. For more information, see Use triggers and functions to implement incremental DDL migration for PostgreSQL databases.
Source Objects	Select one or more objects from the Source Objects section and click the 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.

Advanced Settings

Parameter	Description
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 alerting. Yes: configures alerting. 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, see What is ETL?. Valid values: Yes: configures the ETL feature. You can enter your policy in the code editor. No: does not configure the ETL feature.

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

On the Purchase page, specify the billing method of the change tracking instance. The following table describes the parameters.

Parameter	Description
Billing method	Subscription: You pay for your subscription 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 durations. 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 a pay-as-you-go instance, you can release the instance to reduce costs.
Resource Group Settings	The resource group to which the instance belongs. Default value: default resource group. For more information, see What is Resource Management?
Subscription Duration	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, one year, two years, three years, or five years. Note This parameter is available only if you select the Subscription billing method.

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

For more information about how to create and manage consumer groups, see Create consumer groups.
Use one of the following methods to consume the tracked data: