how to create an RDS PostgreSQL change tracking task - Data Transmission Service

DTS supports creating change tracking tasks for self-managed PostgreSQL and RDS PostgreSQL. This topic uses RDS PostgreSQL as an example to describe the configuration process.

Prerequisites

The source RDS PostgreSQL instance is created. For more information, see Create an RDS PostgreSQL instance.

Note
For supported versions, see Overview of subscription plans.
The parameter wal_level = logical is set for the source RDS PostgreSQL instance. For more information, see Set instance parameters.
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.

Notes

Type	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. WAL logs: Must be enabled. Set the wal_level parameter to logical. DTS requires the WAL logs of the source database to be retained for more than 24 hours. Otherwise, DTS may fail to obtain the WAL logs, which may cause the task to fail. In extreme cases, data inconsistency or loss may occur. The service reliability or performance in the Service Level Agreement (SLA) of DTS may not be guaranteed if the retention period of WAL logs is less than the required period. If the source instance is a read-only or temporary instance, make sure that the instance records transaction logs. To ensure the normal operation of the change tracking task and avoid interruptions caused by primary/secondary switchovers, RDS PostgreSQL must support and enable Logical Replication Slot Failover. For more information, see Logical Replication Slot Failover. Due to the limitations of logical subscriptions on the source database, if a single piece of data that is tracked exceeds 256 MB during the operation of the change tracking instance, the instance may fail and cannot be recovered. You must reconfigure the change tracking instance.
Other limits	If you need to track schema updates (create, delete, and modify operations) on the source instance, create triggers and functions in the source database to capture DDL information. For more information, see Perform DDL incremental migration for PostgreSQL by using triggers and functions. To ensure the accuracy of the change tracking latency display, DTS creates a heartbeat table named dts_postgres_heartbeat in the source database. During incremental data tracking, DTS creates a replication slot with the prefix `dts_sync_` in the source database to replicate data. 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 RDS PostgreSQL instance, you must log on to the secondary instance to clear the replication slot. 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. If a single row of data that you track exceeds 16 MB, the data cannot be consumed. Otherwise, the memory of the consumer client may be out of memory (OOM). 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. Time types with time zones are converted to the corresponding time in the UTC+8 time zone by default. If a DTS task fails to run, DTS technical support will try to restore the task within 8 hours. During the restoration, the task may be restarted, and the parameters of the task may be modified. Note When adjusting parameters, only the parameters of the instance will be modified. The parameters in the database will not be changed.
Special scenarios	If the source instance is RDS PostgreSQL, do not modify the connection address or zone of RDS PostgreSQL during the change tracking process. 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, move the pointer over Data + AI.
3. Choose DTS (DTS) > Change Tracking.
Note
- The actual steps that you need to perform may vary based on the mode and layout of the DMS console. For more information, see Simple mode and Customize the layout and style of the DMS console.
- You can also go to the Change Tracking page of the new DTS console.
Click Create Task to go to the task configuration page.
Optional: In the upper-right corner of the page, click New Configuration Page.
Note
- Skip this step if the Back to Previous Version button is displayed in the upper-right corner of the page.
- Some parameters may differ between the new and previous versions of the configuration page. We recommend that you use the new configuration page.

Configure parameters in the Source Database and Consumer Network Type sections.

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.

Category	Configuration	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 Existing Connection	You can select whether to use an existing database instance based on your business requirements. If you use an existing instance, DTS automatically populates the parameters for the instance. You do not need to enter the parameters again. If you do not use an existing instance, you must configure the database information. Note You can enter the database information in DTS on the Database Connections page or the new configuration page. For more information, see Data Connection Management. The configuration item in the DMS console is Select a DMS database instance.. You can click Add DMS Database Instance or enter the database information in DMS on the home page of the console. For more information, see Enter cloud database information and Enter information about databases that are self-managed or provided by other cloud service providers.
	Database Type	Select PostgreSQL.
	Access Method	Select Cloud Instance.
	Instance Region	Select the region where the RDS PostgreSQL instance resides.
	Replicate Data Across Alibaba Cloud Accounts	Specifies whether to track data across Alibaba Cloud accounts. In this example, No is selected. Important If you want to access cloud resources across Alibaba Cloud accounts, set this parameter to Yes and specify the Alibaba Cloud Account and RAM Role Name parameters. You must configure Resource Access Management (RAM) authorization for the Alibaba Cloud account that is used to configure the DTS task. For more information about how to configure RAM authorization, see Configure RAM authorization for cross-account DTS tasks.
	Instance ID	Select the RDS PostgreSQL instance ID.
	Database Name	Enter the name of the database to be tracked.
	Database Account	Enter the privileged account of RDS PostgreSQL. The account must be the owner (authorized account) of the selected database. For more information about how to create and authorize an account, see Create an account and Create a database.
	Database Password	The password that is used to access the database instance.
	Encryption	Specifies whether to encrypt the connection to the source database. You can configure this parameter based on your business requirements. In this example, Non-encrypted is selected. If you want to establish an SSL-encrypted connection to the source database, perform the following steps: Select SSL-encrypted, upload CA Certificate, Client Certificate, and Private Key of Client Certificate as needed, and then specify Private Key Password of Client Certificate. Note If you set Encryption to SSL-encrypted for a self-managed PostgreSQL database, you must upload CA Certificate. If you want to use the client certificate, you must upload Client Certificate and Private Key of Client Certificate and specify Private Key Password of Client Certificate. For information about how to configure SSL encryption for an ApsaraDB RDS for PostgreSQL instance, see SSL encryption.
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.

Once the configuration is complete, click the Test Connectivity and Proceed button at the bottom of the page.
Note
- Ensure that the IP address range of the DTS service can be automatically or manually added to the security settings of the source database to allow access from DTS servers. For more information, see Add the IP address range of DTS servers.
- If the source database is a self-managed database (the Access Method is not Alibaba Cloud Instance), you must also click Test Connectivity in the CIDR Blocks of DTS Servers dialog box that appears.

Configure the objects for change tracking.

On the Configure Objects page, configure the objects for change tracking.

Configuration	Description
Data Change Types	Data Change Types are selected by default and cannot be modified. 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 need to track Schema Updates, create triggers and functions in the source database to capture DDL information. For more information, see Perform DDL incremental migration for PostgreSQL by using triggers and functions.
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.

Click Next: Advanced Settings to configure advanced settings.

Configuration	Description
Dedicated Cluster for Task Scheduling	By default, DTS schedules the task to a shared cluster. You do not need to configure this parameter. You can purchase dedicated clusters of specified specifications to run DTS change tracking tasks. For more information, see What is a DTS dedicated cluster.
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: 720. We recommend that you set the parameter to a value greater than 30. If DTS is reconnected to the source database instance within the specified time range, DTS resumes the change tracking task. Otherwise, the change tracking task fails. Note If multiple change tracking tasks are configured for a database instance, the shortest retry time range takes precedence. For example, Task A and Task B are configured for the same database instance. Task A is configured with a retry time range of 30 minutes, and Task B is configured with a retry time range of 60 minutes. In this case, the retry time range of 30 minutes takes precedence. When DTS retries a connection, fees are charged. We recommend that you specify the retry time range based on your business requirements, or release the DTS instance at the earliest opportunity after the source database instance is released.
Retry Time for Other Issues	The retry time range for other issues. For example, if DDL or DML operations fail to be performed after the change tracking task is started, DTS immediately retries the operations within the retry time range. Valid values: 1 to 1440. Unit: minutes. Default value: 10. We recommend that you set the parameter to a value greater than 10. If the failed operations are successfully performed within the specified retry time range, DTS resumes the change tracking task. Otherwise, the change tracking task fails. Important The value of the Retry Time for Other Issues parameter must be smaller than the value of the Retry Time for Failed Connections parameter.
Environment Tag	You can select an environment tag based on your business requirements. In this example, no environment tag is selected.
Monitoring and Alerting	Specifies whether to enable alerting for the change tracking task. If alerting is configured and the task fails or the latency exceeds the threshold, alert notifications are sent. Valid values: No: does not enable alerting. Yes: enables alerting. In this case, you must also configure the alert threshold and alert notification settings. For more information, see Configure monitoring and alerting when you create a DTS task.

In the lower part of the page, click Next: Save Task Settings and Precheck.
- To view the parameters to be specified when you call the relevant API operation to configure the DTS task, move the pointer over Next: Save Task Settings and Precheck and click Preview OpenAPI parameters.
- If you do not need to view or have viewed the parameters, 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, 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.

Purchase an instance.

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: