Migrate data from a TiDB database to an ApsaraDB RDS for MySQL instance - Data Transmission Service

This topic describes how to migrate data from a TiDB database to an ApsaraDB RDS for MySQL instance by using Data Transmission Service (DTS).

Prerequisites

The destination ApsaraDB RDS for MySQL instance is created. The available storage space of the instance is larger than the total size of data in the source TiDB database. For more information, see Create an ApsaraDB RDS for MySQL instance.
Preparations (optional) are made to collect incremental data if you want to migrate incremental data from the TiDB database.

Preparations (optional)

You can use one of the following methods to collect incremental data from the TiDB database:

Use TiDB Binlog

Note

The server on which the source database is deployed must be in the same internal network as the servers on which Pump, Drainer, and the Kafka cluster are deployed. This minimizes the impact of network latency on incremental data migration.

Prepare a Kafka cluster or instance by using one of the following methods.
- Deploy a self-managed Kafka cluster. For more information, visit the Apache Kafka official website.
  Warning
  We recommend that you set the message.max.bytes and replica.fetch.max.bytes parameters for the Kafka broker and the fetch.message.max.bytes parameter for the Kafka consumer to greater values. This ensures that the Kafka cluster can receive a larger amount of binary log data from the TiDB database. For more information, see CONFIGURATION.
- Create an ApsaraMQ for Kafka instance. For more information, see Overview.
  Note
  The ApsaraMQ for Kafka instance must be deployed in the same virtual private cloud (VPC) as the source database server. This ensures reliable data transmission and minimizes the impact of network latency on incremental data migration.
Create a topic in the self-managed Kafka cluster or the ApsaraMQ for Kafka instance.
Important
To ensure that incremental data can be replicated to the partition whose ID is 0, make sure that the topic contains only one partition.
Deploy Pump and Drainer. For more information, see TiDB Binlog Cluster Deployment.
Modify the configuration file of Drainer and specify a Kafka cluster to receive data from Drainer. For more information, see Binlog Consumer Client User Guide.
Note
Make sure that the server on which the TiDB database is deployed can connect to the Kafka cluster.
Add the CIDR blocks of DTS servers to a whitelist of the TiDB database. For more information, see Add the CIDR blocks of DTS servers.

Use TiCDC

Prepare a Kafka cluster or instance by using one of the following methods.
- Deploy a self-managed Kafka cluster. For more information, visit the Apache Kafka official website.
  Warning
  We recommend that you set the message.max.bytes and replica.fetch.max.bytes parameters for the Kafka broker and the fetch.message.max.bytes parameter for the Kafka consumer to greater values. This ensures that the Kafka cluster can receive a larger amount of binary log data from the TiDB database. For more information, see CONFIGURATION.
- Create an ApsaraMQ for Kafka instance. For more information, see Overview.
  Note
  The ApsaraMQ for Kafka instance must be deployed in the same virtual private cloud (VPC) as the source database server. This ensures reliable data transmission and minimizes the impact of network latency on incremental data migration.
Create a topic in the self-managed Kafka cluster or the ApsaraMQ for Kafka instance.
Important
To ensure that incremental data can be replicated to the partition whose ID is 0, make sure that the topic contains only one partition.
Install TiCDC. For more information, see Deploy and Maintain TiCDC.
Note
We recommend that you use TiUP to add a new TiCDC node or scale out the existing TiCDC node in the TiDB cluster.
Replicate the incremental data in the source TiDB database to Kafka. For more information, see Replicate Data to Kafka.
Note
- Make sure that the server on which the TiDB database is deployed can connect to the Kafka cluster.
- We recommend that you use tiup cdc cli changefeed create \ in the first command line.

Usage notes

Category	Description
Limits on the source database	The server on which the source database is deployed must have sufficient outbound bandwidth. Otherwise, the data migration speed decreases. The tables to be migrated must have PRIMARY KEY or UNIQUE constraints and all fields must be unique. Otherwise, the destination database may contain duplicate data records. If you select tables as the objects to be migrated and you want to modify the tables in the destination database, such as renaming tables or columns, you can migrate up to 1,000 tables in a single data migration task. If you run a task to migrate more than 1,000 tables, a request error occurs. In this case, we recommend that you configure multiple tasks to migrate the tables in batches or configure a task to migrate the entire database. If you want to migrate incremental data from the source TiDB database, you must deploy a Kafka cluster and install related components for the TiDB database to collect the incremental data.
Other limits	During incremental data migration, DTS can obtain data only from the partition whose ID is 0 in the destination topic. If the data migration task involves incremental data migration, you must perform the required operations on the source database or insert test data in a timely manner after the task is created. This ensures that the offset information of the task is updated. Otherwise, the task may fail due to excessive latency. If the data to be migrated contains information such as rare characters or emojis that takes up four bytes, the destination databases and tables to receive the data must use UTF8mb4 character set. Note If you use the schema migration feature of DTS, set the instance parameter `character_set_server` in the destination database to UTF8mb4 character set. If you write column names that differ only in capitalization to the same table in the destination MySQL database, the data migration result may not meet your expectations because the column names in MySQL databases are not case-sensitive. After data migration is complete, that is, the Status of the instance changes to Completed, we recommend that you run the `analyze table <table name>` command to check whether data is written to the destination table. For example, if a high-availability (HA) switchover is triggered in the destination MySQL database, data may be written only to the memory. As a result, data loss occurs. If the name of the database to be migrated to the destination ApsaraDB RDS for MySQL instance does not comply with the database naming conventions of ApsaraDB RDS for MySQL, you must create a database in the destination ApsaraDB RDS for MySQL instance before you configure a data migration task. Then, you can use the object name mapping feature to rename the database when you configure the data migration task. For more information, see Manage databases and Map object names. During full data migration, DTS uses the read and write resources of the source and destination databases. This may increase the loads of the database servers. Before you migrate data, evaluate the impact of data migration on the performance of the source and destination databases. We recommend that you migrate data during off-peak hours, such as when the CPU load of the source and destination databases is less than 30%. During full data migration, concurrent INSERT operations cause fragmentation in the tables of the destination database. After full data migration is complete, the size of used tablespace of the destination database is larger than that of the source database. Data inconsistency between the source and destination databases may occur if data from other sources is written to the destination database during data migration. 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. You must check whether the precision settings meet your business requirements. DTS attempts to resume data migration tasks that failed within the last seven days. Before you switch workloads to the destination database, you must stop or release the failed tasks. You can also execute the `REVOKE` statement to revoke the write permissions from the accounts that are used by DTS to access the destination database. Otherwise, the data in the source database overwrites the data in the destination database after a failed task is resumed. If DDL statements fail to be executed in the destination database, the DTS task continues to run. You can view the DDL statements that fail to be executed in task logs. For more information about how to view task logs, see View task logs. 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 Only the parameters of the task may be modified. The parameters of databases are not modified. The parameters that may be modified include but are not limited to the parameters in the "Modify instance parameters" section of the Modify the parameters of a DTS instance topic.

Billing

Migration type	Instance configuration fee	Internet traffic fee
Schema migration and full data migration	Free of charge.	When the Access Method parameter of the destination database is set to Public IP Address, you are charged for Internet traffic. For more information, see Billing overview.
Incremental data migration	Charged. For more information, see Billing overview.

SQL operations that support incremental migration

Operation type	SQL statement
DML	INSERT, UPDATE, and DELETE
DDL	CREATE TABLE, DROP TABLE, ALTER TABLE, RENAME TABLE, TRUNCATE TABLE, CREATE VIEW, DROP VIEW, and ALTER VIEW

Permissions required for database accounts

Database	Required permissions	References
TiDB database	The SELECT permission on objects to migrate and the SHOW VIEW permission	Privilege Management
ApsaraDB RDS for MySQL instance	The read and write permissions on the destination database	Create an account and Modify the permissions of an account

Procedure

Use one of the following methods to go to the Data Migration page and select the region in which the data migration instance resides.
DTS console
1. Log on to the DTS console.
2. In the left-side navigation pane, click Data Migration.
3. In the upper-left corner of the page, select the region in which the data migration instance resides.
DMS console
Note
The actual operation 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.
1. Log on to the DMS console.
2. In the top navigation bar, move the pointer over Data + AI > DTS (DTS) > Data Migration .
3. From the drop-down list to the right of Data Migration Tasks, select the region in which the data synchronization instance resides.
Click Create Task to go to the task configuration page.

Configure the source and destination databases. The following table describes the parameters.

Section	Parameter	Description
N/A	Task Name	The name of the DTS task. DTS automatically generates a task name. We recommend that you specify a descriptive name that makes it easy to identify the task. You do not need to specify a unique task name.
Source Database	Select Existing Connection	If you use a database instance that is registered with DTS, select the instance from the drop-down list. DTS automatically populates the following database parameters for the instance. For more information, see Manage database connections. Note In the DMS console, you can select the database instance from the Select a DMS database instance drop-down list. If you fail to register the instance with DTS, or you do not need to use the instance that is registered with DTS, you must configure the following database information.
	Database Type	The type of the source database. Select TiDB.
	Access Method	The access method of the source database. Select an access method based on the deployment location of the TiDB database. In this example, select Self-managed Database on ECS. Note If you set this parameter to other values, you must prepare the environment that is required for the self-managed database before data migration. For more information, see Preparation overview.
	Instance Region	The region in which the TiDB database resides.
	ECS Instance ID	The ID of the ECS instance that hosts the TiDB database.
	Port Number	The service port number of the source TiDB database. Default value: 4000.
	Database Account	The account of the TiDB database. For more information about the permissions required for the account, see the Permissions required for database accounts section of this topic.
	Database Password	The password that is used to access the database.
	Migrate Incremental Data	Specifies whether to migrate the incremental data of the TiDB database. Configure this parameter based on your business requirements. Note If you want to migrate incremental data from the TiDB database, select Yes and enter the Kafka cluster information. For more information, see the Kafka cluster section of this topic.
Destination Database	Select Existing Connection	If you use a database instance that is registered with DTS, select the instance from the drop-down list. DTS automatically populates the following database parameters for the instance. For more information, see Manage database connections. Note In the DMS console, you can select the database instance from the Select a DMS database instance drop-down list. If you fail to register the instance with DTS, or you do not need to use the instance that is registered with DTS, you must configure the following database information.
	Database Type	The type of the destination database. Select MySQL.
	Access Method	The access method of the destination database. Select Alibaba Cloud Instance.
	Instance Region	The region in which the destination ApsaraDB RDS for MySQL instance resides.
	Replicate Data Across Alibaba Cloud Accounts	In this example, a database instance of the current Alibaba Cloud account is used. Select No.
	RDS Instance ID	The ID of the destination ApsaraDB RDS for MySQL instance.
	Database Account	The database account of the destination ApsaraDB RDS for MySQL instance. For more information about the permissions that are required for the account, see the Permissions required for database accounts section of this topic.
	Database Password	The password that is used to access the database instance.
	Encryption	Specifies whether to encrypt the connection to the database. You can select Non-encrypted or SSL-encrypted based on your business requirements. If you want to set this parameter to SSL-encrypted, you must enable SSL encryption for the ApsaraDB RDS for MySQL instance before you configure the DTS task. For more information, see Use a cloud certificate to enable SSL encryption.

In the lower part of the page, click Test Connectivity and Proceed, and then click Test Connectivity in the CIDR Blocks of DTS Servers dialog box that appears.
Note
Make sure that the CIDR blocks of DTS servers can be automatically or manually added to the security settings of the source and destination databases to allow access from DTS servers. For more information, see Add the CIDR blocks of DTS servers.

Configure the objects to be migrated.

On the Configure Objects page, configure the objects that you want to migrate.

Parameter	Description
Migration Types	To perform only full data migration, select Schema Migration and Full Data Migration. To ensure service continuity during data migration, select Schema Migration, Full Data Migration, and Incremental Data Migration. Note If you do not select Schema Migration, make sure a database and a table are created in the destination database to receive data and the object name mapping feature is enabled in Selected Objects. If you do not select Incremental Data Migration, we recommend that you do not write data to the source database during data migration. This ensures data consistency between the source and destination databases.
Processing Mode of Conflicting Tables	Precheck and Report Errors: checks whether the destination database contains tables that use the same names as tables in the source database. If the source and destination databases do not contain tables that have identical table names, the precheck is passed. Otherwise, an error is returned during the precheck and the data migration task cannot be started. Note If the source and destination databases contain tables with identical names and the tables in the destination database cannot be deleted or renamed, you can use the object name mapping feature to rename the tables that are migrated to the destination database. For more information, see Map object names. Ignore Errors and Proceed: skips the precheck for identical table names in the source and destination databases. Warning If you select Ignore Errors and Proceed, data inconsistency may occur and your business may be exposed to the following potential risks: If the source and destination databases have the same schema, and a data record has the same primary key as an existing data record in the destination database, the following scenarios may occur: During full data migration, DTS does not migrate the data record to the destination database. The existing data record in the destination database is retained. During incremental data migration, DTS migrates the data record to the destination database. The existing data record in the destination database is overwritten. If the source and destination databases have different schemas, only specific columns are migrated or the data migration task fails. Proceed with caution.
Capitalization of Object Names in Destination Instance	The capitalization of database names, table names, and column names in the destination instance. By default, DTS default policy is selected. You can select other options to make sure that the capitalization of object names is consistent with that of the source or destination database. For more information, see Specify the capitalization of object names in the destination instance.
Source Objects	Select one or more objects from the Source Objects section. Click the icon to add the objects to the Selected Objects section. Note You can select tables or databases as the objects to be migrated.
Selected Objects	To rename an object that you want to migrate to the destination instance, right-click the object in the Selected Objects section. For more information, see Map the name of a single object. To rename multiple objects at a time, click Batch Edit in the upper-right corner of the Selected Objects section. For more information, see Map multiple object names at a time. Note To specify WHERE conditions to filter data, right-click a table in the Selected Objects section. In the dialog box that appears, Specify filter conditions. If you use the object name mapping feature to rename an object, other objects that are dependent on the object may fail to be migrated.

Click Next: Advanced Settings to configure advanced settings.

Parameter	Description
Retry Time for Failed Connections	The retry time range for failed connections. If the source or destination database fails to be connected after the data migration task is started, DTS immediately retries a connection within the retry time range. Valid values: 10 to 1,440. 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 and destination databases within the specified retry time range, DTS resumes the data migration task. Otherwise, the data migration task fails. Note If you specify different retry time ranges for multiple data migration tasks that share the same source or destination database, the value that is specified later 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 the earliest opportunity after the source database and destination instance are 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 data migration 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 data migration task. Otherwise, the data migration 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.
Enable Throttling for Full Data Migration	Specifies whether to enable throttling for full data migration. During full data migration, DTS uses the read and write resources of the source and destination databases. This may increase the loads of the database servers. You can enable throttling for full data migration based on your business requirements. To configure throttling, you must configure the Queries per second (QPS) to the source database, RPS of Full Data Migration, and Data migration speed for full migration (MB/s) parameters. This reduces the loads of the destination database server. Note You can configure this parameter only if you select Full Data Migration for the Migration Types parameter.
Enable Throttling for Incremental Data Migration	Specifies whether to enable throttling for incremental data migration. To configure throttling, you must configure the RPS of Incremental Data Migration and Data migration speed for incremental migration (MB/s) parameters. This reduces the loads of the destination database server. Note You can configure this parameter only if you select Incremental Data Migration for the Migration Types parameter.
Environment Tag	The environment tag that is used to identify the DTS instance. You can select an environment tag based on your business requirements. In this example, you do not need to configure this parameter.
Configure ETL	Specifies whether to enable the extract, transform, and load (ETL) feature. For more information, see What is ETL? Valid values: Yes: configures the ETL feature. You can enter data processing statements in the code editor. For more information, see Configure ETL in a data migration or data synchronization task. No: does not configure the ETL feature.
Monitoring and Alerting	Specifies whether to configure alerting for the data migration task. If the task fails or the migration latency exceeds the specified threshold, the alert contacts receive notifications. Valid values: No: does not configure alerting. Yes: configures alerting. In this case, you must also configure the alert threshold and alert notification settings. For more information, see the Configure monitoring and alerting when you create a DTS task section of the Configure monitoring and alerting topic.

Click Next Step: Data Verification to configure the data verification task.
For more information about how to use the data verification feature, see Configure a data verification task.

Save the task settings and run a 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 data migration task, DTS performs a precheck. You can start the data migration 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 analyze the causes based on the check results, troubleshoot the issues. Then, run a precheck again.
- If an alert is triggered for an item during the precheck:
  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 Instance page, configure the Instance Class parameter for the data migration instance. The following table describes the parameters.

Section	Parameter	Description
New Instance Class	Resource Group	The resource group to which the data migration instance belongs. Default value: default resource group. For more information, see What is Resource Management?
New Instance Class	Instance Class	DTS provides instance classes that vary in the migration speed. You can select an instance class based on your business scenario. For more information, see Instance classes of data migration instances.

Read and agree to Data Transmission Service (Pay-as-you-go) Service Terms by selecting the check box.
Click Buy and Start. In the message that appears, click OK.
You can view the progress of the task on the Data Migration page.
Note
- If a data migration task cannot be used to migrate incremental data, the task automatically stops. The Completed is displayed in the Status section.
- If a data migration task can be used to migrate incremental data, the task does not automatically stop. The incremental data migration task never stops or completes. The Running is displayed in the Status section.

Kafka cluster

Parameter	Description
Kafka Cluster Type	The type of the Kafka cluster. Configure this parameter based on the deployment location of the Kafka cluster. In this example, select Self-managed Database on ECS. Note If you select Express Connect, VPN Gateway, or Smart Access Gateway, you must also select a VPC from the Connected VPC drop-down list and specify Domain Name or IP.
Kafka Data Source Component	Select Use the default binlog format of the TiDB database. or Use the TiCDC Canal-JSON format. based on the preparations you made.
ECS Instance ID	The ID of the ECS instance to which the Kafka cluster belongs.
Port Number	The service port of the Kafka cluster.
Kafka Cluster Account	The username and password of the Kafka cluster. If authentication is not enabled for the Kafka cluster, you do not need to configure this parameter.
Kafka Cluster Password
Kafka Version	The Kafka cluster version. Note If the Kafka cluster version is 1.0 or later, select 1.0.
Encryption	Specifies whether to encrypt the connection to the Kafka cluster. Select Non-encrypted or SCRAM-SHA-256 based on your business and security requirements.
Topic	The topic to which the incremental data belongs.