How to create a PolarDB for MySQL change tracking task - Data Transmission Service

The change tracking feature allows you to subscribe to incremental data in real-time, facilitating lightweight cache updates, asynchronous decoupling, and real-time data synchronization using ETL logic. This topic explains the process of creating a PolarDB for MySQL change tracking task.

Prerequisites

A PolarDB for MySQL cluster has been successfully created. For more information, see how to customize your purchase and how to purchase a subscription cluster.
Currently, PolarDB for MySQL instances support versions 5.6, 5.7, and 8.0.
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 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. Binary logs: Binary logs must be enabled, and loose_polar_log_bin must be set to on. Otherwise, an error is reported during the precheck phase, and the change tracking task cannot be started. DTS requires that the local binary logs of the source database be retained for more than 24 hours. Otherwise, DTS may fail to obtain the binary logs, which may cause the task to fail. In extreme cases, data inconsistency or loss may occur. Issues that occur because the retention period of binary logs is shorter than required by DTS are not covered under the DTS Service Level Agreement (SLA). If the source instance is a read-only or temporary instance, make sure that the instance records transaction logs.
Other limits	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. DTS does not track the DDL operations that are performed by using pt-online-schema-change. Therefore, the change tracking client may fail to write the consumed data to the destination tables due to schema conflicts. If the size of a single row of data that you track exceeds 16 MB, you cannot consume the row of data. Otherwise, an out of memory (OOM) error may occur on the change tracking client.

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 specify 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 parameters for the instance. Note You can enter the database into 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 into DMS on the home page of the console. For more information, see Enter a cloud database and Enter a self-managed database.
	Database Type	Select PolarDB for MySQL.
	Access Method	Select Cloud Instance.
	Instance Region	Select the region where the PolarDB for MySQL cluster 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.
	Polardb Instance ID	Select the PolarDB for MySQL cluster ID.
	Database Account	Enter the Read-only Account of the PolarDB for MySQL database or a custom account that has the REPLICATION CLIENT, REPLICATION SLAVE, SHOW VIEW, and SELECT permissions.
	Database Password	The password that is used to access the database instance.
	Encryption	You can specify this option based on your business requirements. For more information about the SSL encryption feature, see Set 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.

After the configuration is complete, click Test Connectivity and Proceed 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.

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 is 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.
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, you do not need to configure this parameter.
Whether to delete SQL operations on heartbeat tables of forward and reverse tasks	Specifies whether to write SQL operations on heartbeat tables to the source database while the DTS instance is running. Valid values: Yes: does not write SQL operations on heartbeat tables. In this case, a latency of the DTS instance may be displayed. No: writes SQL operations on heartbeat tables. In this case, features such as physical backup and cloning of the source database may be affected.
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: