Track data changes from a DMS logical database - Data Transmission Service

This topic describes how to track data changes from a Data Management (DMS) logical database by using Data Transmission Service (DTS).

Prerequisites

A DMS logical database is configured. For more information, see Logical database.

Note A DMS logical database is created based on the database shards of multiple PolarDB for MySQL clusters.

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 binary logs must be met: The binary logging feature must be enabled. The value of the binlog_row_image parameter must be set to full. The binary logs of the source database must be stored for more than 24 hours. Otherwise, DTS may fail to obtain the binary logs and the task may fail. In exceptional circumstances, data inconsistency or loss may occur. Make sure that you set the retention period of binary 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.
Other limits	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 the 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. An internal endpoint is configured for the ApsaraDB RDS for MySQL instance.

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 Configure the DMS console based on your business requirements.
- 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, configure the source database and the consumer network type.

Warning After you select the source instance, we recommend that you read the limits displayed in the upper part of the page. This helps you create and run the change tracking task.


Section	Parameter	Description
None	Task Name	The task name that DTS automatically generates. 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 Instance	The instance that you want to use. You can choose whether to select an existing instance based on your business requirements. If you use an existing instance, DTS automatically applies the parameter settings of the instance. Note To modify the connection settings of a template, you can edit the template when you configure the Select Instance parameter in the Source Database section. To edit the template name, you can click Edit Template in the lower part of the Source Database section. The modified connection template takes 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 an existing instance, you must configure the following parameters.
	Database Type	The type of the source database. Select DMS LogicDB.
	Access Method	The service that is used to access the source database. Select Alibaba Cloud Instance.
	Instance Region	The region in which the DMS logical database resides.
	DMS LogicDB	Select the name of the DMS logical database.
	Database Account	The account of the source database. Enter the username that is used to access the DMS logical database. The PolarDB for MySQL clusters that host the DMS physical databases must share the same username and password. Each cluster must have read permissions on the corresponding physical database. For more information, see Create a database account.
	Database Password	The password of the database account.
Consumer Network Type	Network Type	The Network Type parameter is set to VPC. You must select a VPC and a vSwitch. For more information, see VPCs. Note After the task is created, 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 as 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.
Warning
- If the source or destination database instance is an Alibaba Cloud database instance, such as an ApsaraDB RDS for MySQL or ApsaraDB for MongoDB instance, or is a self-managed database hosted on ECS, DTS automatically adds the CIDR blocks of DTS servers to the whitelist of the database instance or ECS security group rules. For more information, see Add the CIDR blocks of DTS servers to the security settings of on-premises databases. If the source or destination database is a self-managed database on data centers or is from other cloud service providers, you must manually add the CIDR blocks of DTS servers to allow DTS to access the database.
- If the CIDR blocks of DTS servers are automatically or manually added to the whitelist of the database, Alibaba Cloud database instance, or ECS security group rules, security risks may arise. Therefore, before you use DTS to migrate data, 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 ECS security group rules and forbidding unauthorized CIDR blocks, or connecting the database to DTS by using Express Connect, VPN Gateway, or Smart Access Gateway.
- After the DTS task is complete or released, we recommend that you manually detect and remove the added CIDR blocks from the whitelist of the database, Alibaba Cloud database instance, or ECS security group rules.

Select objects for the task and configure 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 Updates 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 required data.
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 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	Select 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. Valid values: No: does not set alerts. Yes: sets alerts. In this case, you must also set the alert threshold and alert contacts.
Retry Time for Failed Connections	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 an instance serves as the source database of multiple change tracking tasks, the less value of this parameter 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: Yes: configures the ETL feature. You can enter data processing statements 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.
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 the icon next to each failed item to view details.
  After you troubleshoot the issues based on the causes, run a precheck again.
  If you do not need to troubleshoot the issues, ignore failed items and run a precheck again.
Wait until the Success Rate becomes 100%. Then, click Next: Purchase Instance.

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 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. You are offered lower prices for longer subscription periods. 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 it to reduce costs.
Billing Type of Change Tracking Instance	If you select the subscription billing method, Billing Type for Change Tracking Instance is set to USD 120 per month for configuration fee (no data traffic fee).
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.

Read and select 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: