Data Transmission Service:Migrate data from a PolarDB for MySQL cluster to an ApsaraDB for SelectDB instance

Prerequisites

The source PolarDB for MySQL cluster and destination ApsaraDB for SelectDB instance are created. For more information, see Create an instance.

Precautions

Billing

SQL operations that support incremental migration

Permissions required for database accounts

For information about how to create a database account and grant permissions to the account, see the following topics:

• For a PolarDB for MySQL cluster, see Create and manage database accounts and Manage the password of a database account.

• For a SelectDB instance, see Cluster permission management and Basic permission management.

Procedure

1. 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.

2. Click Create Task to go to the task configuration page.

3. 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 PolarDB for MySQL.
   	Access Method	The access method of the source database. Select Alibaba Cloud Instance.
   	Instance Region	The region in which the source PolarDB for MySQL cluster resides.
   	Replicate Data Across Alibaba Cloud Accounts	Specifies whether to migrate data across Alibaba Cloud accounts. In this example, No is selected. Note If you want to configure a data migration task between different Alibaba Cloud accounts, you must first configure Resource Access Management (RAM) authorization.
   	PolarDB Cluster ID	The ID of the source PolarDB for MySQL cluster.
   	Database Account	The database account of the source PolarDB for MySQL cluster. For more information about the permissions that are required for the database account, see the Permissions required for database accounts section of this topic.
   	Database Password	The password that is used to access the database.
   	Encryption	Specifies whether to encrypt the connection to the source database. You can set this parameter based on your business requirements. For more information about the SSL encryption feature, see Configure SSL encryption.
   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 SelectDB.
   	Access Method	The access method of the destination database. Select Alibaba Cloud Instance.
   	Instance Region	The region in which the destination SelectDB instance resides.
   	Replicate Data Across Alibaba Cloud Accounts	Specifies whether to migrate data across Alibaba Cloud accounts. In this example, No is selected.
   	Instance ID	The ID of the destination ApsaraDB for SelectDB instance.
   	Database Account	The database account of the destination ApsaraDB for SelectDB instance. For information about the permissions that are required for the database account, see the Permissions required for database accounts section of this topic.
   	Database Password	The password that is used to access the database.

4. In the lower part of the page, click Test Connectivity and Proceed.

   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.

5. Configure the objects to be migrated.

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

      Parameter	Description
      Migration Types	To perform only full data migration, select both Schema Migration and Full Data Migration. To migrate data without service downtime, select Schema Migration, Full Data Migration, and Incremental Data Migration. Important When data is migrated from a PolarDB for MySQL cluster to a SelectDB instance, data type conversion is performed. If you do not select Schema Migration, you must create tables that use the Unique or Duplicate key model in the destination SelectDB instance before data migration. For more information, see Data type mapping, Additional column information, and Data model. To ensure data consistency, do not write data to the source database during data migration if Incremental Data Migration is not selected.
      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 columns, tables, or databases as the objects to be migrated.
      Selected Objects	To change a table name to be used in the destination project, right-click the table in the Selected Objects section. For more information, see Map object names. If you select Schema Migration for the Migration Types parameter, you can select only tables as the objects to be migrated and the bucket_count parameter must be set. Right-click a table to be migrated in the Selected Objects section, select Yes for the Enable Parameter Settings parameter in the Parameter Settings section that appears, specify Value based on your business requirements, and click OK. Note To select the SQL operations performed on a specific database or table, right-click the object in the Selected Objects section. In the dialog box that appears, select the SQL operations that you want to migrate. For more information, see the SQL operations that support incremental migration section of this topic. To specify WHERE conditions to filter data, right-click a table in the Selected Objects section. In the dialog box that appears, specify the conditions. For more information, see 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.

   2. Click Next: Advanced Settings to configure advanced settings.

      Parameter	Description
      Dedicated Cluster for Task Scheduling	By default, DTS schedules the data migration task to the shared cluster if you do not specify a dedicated cluster. If you want to improve the stability of data migration tasks, purchase a dedicated cluster. For more information, see What is a DTS dedicated cluster.
      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, no environment tag is selected.
      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.
      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.

   3. Optional. In the lower part of the page, click Next: Configure Database and Table Fields. In the dialog box that appears, specify Primary Key Column, Distribution Key, and Engine for the tables that you want to migrate.

      Note

      • This step is available only if you select Schema Migration for the Migration Types parameter. You can set the Definition Status parameter to All and modify the database and table fields.

      • You can select multiple columns for the Primary Key Column parameter from the drop-down list. One or more columns specified for the Primary Key Column parameter can be selected for the Distribution Key parameter.

      • If the table does not have primary keys or UNIQUE constraints, select duplicate for the Engine parameter. Otherwise, the data migration task may fail or data loss may occur.

6. 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.

7. Purchase a DTS instance.

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

   2. 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?
      	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.

   3. Read and agree to Data Transmission Service (Pay-as-you-go) Service Terms by selecting the check box.

   4. 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.

Data type mappings

Additional column information