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Data Transmission Service:Migrate data from a PolarDB for MySQL cluster to a PolarDB-X 2.0 instance

Last Updated:Jul 01, 2025

You can migrate data from a PolarDB for MySQL cluster to a PolarDB-X 2.0 instance by using Data Transmission Service (DTS).

Prerequisites

  • A PolarDB-X 2.0 instance is created.

  • The available storage space of the PolarDB-X 2.0 instance is larger than the total size of the data in the PolarDB for MySQL cluster.

Limits

Note
  • During schema migration, DTS migrates foreign keys from the source database to the destination database.

  • During full data migration and incremental data migration, DTS temporarily disables the constraint check and cascade operations on foreign keys at the session level. If you perform the cascade update and delete operations on the source database during data migration, data inconsistency may occur.

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 need to edit 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 or configure a task to migrate the entire database.

  • If you need to migrate incremental data:

    • The binary logging feature must be enabled and the loose_polar_log_bin parameter must be set to on. Otherwise, error messages are returned during the precheck and the data migration task fails to be started. For more information, see Enable binary logging and Modify parameters.

      Note

      If you enable the binary logging feature for a PolarDB for MySQL cluster, you are charged for the storage space that is occupied by binary logs.

    • The binary logs of a PolarDB for MySQL cluster must be stored for at least three days. We recommend that you store the binary logs seven days. 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 configure the retention period of binary logs based on the preceding requirements. Otherwise, the service reliability or performance stated in the Service Level Agreement (SLA) of DTS may not be guaranteed.

      Note

      For more information about how to set retention period of the binary logs of a PolarDB for MySQL cluster, see Modify the retention period.

  • Limits on operations to be performed on the source database:

    • During full data migration, do not perform DDL operations to change the schemas of databases or tables. Otherwise, the data migration task fails.

    • If you perform only full data migration, do not write data to the source database during data migration. Otherwise, data inconsistency between the source and destination databases occurs. To ensure data consistency, we recommend that you select full data migration and incremental data migration as the migration types.

    • Incremental DDL operations cannot be migrated. If you perform DDL operations on the source database during incremental data migration, the data migration task fails. If you need to perform DDL operations, we recommend that you perform the operations in the destination database and then perform the operations in the source database.

Other limits

  • DTS does not migrate the read-only nodes of the source PolarDB for MySQL cluster.

  • DTS does not migrate Object Storage Service (OSS) external tables from the source PolarDB for MySQL cluster.

  • 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. 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.

  • 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.

  • 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 value, DTS sets the precision for the FLOAT data type to 38 digits and the precision for the DOUBLE data type to 308 digits.

  • 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.

  • DTS executes the CREATE DATABASE IF NOT EXISTS `test` statement in the source database as scheduled to move forward the binary log file position.

  • 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.

Migration types

  • Schema migration

    Data Transmission Service (DTS) migrates the schemas of the selected objects from the source database to the destination database.

    Note
    • DTS supports schema migration for the following types of objects: tables, views, triggers, stored procedures, and stored functions.

      Note

      The routine_body of the stored procedure, routine_body of the stored functions, and select_statement of the views cannot be modified during the migration.

    • During schema migration, DTS changes the value of the SECURITY attribute from DEFINER to INVOKER for views, stored procedures, and functions. In addition, DTS sets the DEFINER to the destination database account used in the migration.

      Note

      The SECURITY attribute and DEFINER cannot be modified during the migration.

    • DTS does not migrate user information. To call a view, stored procedure, or stored function of the destination database, you must grant the read and write permissions to INVOKER.

  • Full data migration

    DTS migrates the historical data of required objects from the source database to the destination database.

  • Incremental data migration

    After full data migration is complete, DTS migrates incremental data from the source database to the destination database. Incremental data migration allows data to be migrated smoothly without interrupting the services of self-managed applications during data migration.

SQL operations that can be migrated during incremental data migration

INSERT, UPDATE, and DELETE

Permissions required for database accounts

Database

Required permission

PolarDB for MySQL cluster

Read permissions on the objects to be migrated

PolarDB-X 2.0 instance

Read and write permissions on the objects to be migrated

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

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.

    Warning

    After you configure the source and destination databases, we recommend that you read the Limits that are displayed in the upper part of the page. Otherwise, the task may fail or data inconsistency may occur.

    Section

    Parameter

    Description

    N/A

    Task Name

    The name of the DTS task. DTS automatically generates a task name. We recommend that you specify an informative 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.

    PolarDB Instance 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 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 source database. You can configure 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 PolarDB-X 2.0.

    Access Method

    The access method of the destination instance. Select Alibaba Cloud Instance.

    Instance Region

    The region in which the PolarDB-X 2.0 instance resides.

    Instance ID

    The ID of the destination PolarDB-X 2.0 instance.

    Database Account

    The database account of the destination PolarDB-X 2.0 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.

  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 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.

      Source Objects

      Select one or more objects from the Source Objects section. Click the Rightwards arrow icon and add the objects to the Selected Objects section.

      Note

      You can select columns, tables, or schemas as the objects to be migrated. If you select tables or columns as the objects to be migrated, DTS does not migrate other objects, such as views, triggers, or stored procedures, to the destination database.

      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
      • 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.

      • To specify WHERE conditions to filter data, right-click an object in the Selected Objects section. In the dialog box that appears, specify the conditions. For more information, see Specify filter conditions.

      • To select the SQL operations performed on a specific database or table, right-click an object in the Selected Objects section. In the dialog box that appears, select the SQL operations that you want to migrate.

    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, you do not need to select an environment tag.

      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:

      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:

    3. 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.

  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 data migration 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.