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    PolarDB:Migrate a self-managed MySQL database to PolarDB for MySQL

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    PolarDB:Migrate a self-managed MySQL database to PolarDB for MySQL

    Last Updated:Apr 18, 2026

    You can use Data Transmission Service (DTS) to migrate your self-managed MySQL database to a PolarDB for MySQL cluster.

    Prerequisites

    Important notes

    Note

    • DTS migrates foreign keys from the source database to the destination database during schema migration.

    • During full and incremental migration, DTS temporarily disables constraint checks and foreign key cascade operations at the session level. If cascading updates or deletes occur in the source database while the task is running, this may cause data inconsistency.

    Type

    Description

    Source database limits

    • Bandwidth requirement: The server hosting the source database must have sufficient outbound bandwidth. Otherwise, migration speed will drop.

    • Each table to migrate must have a primary key or UNIQUE constraint, and the key columns must contain unique values. Otherwise, duplicate records may appear in the destination database.

    • If you select tables as the migration objects and edit them—for example, by mapping column names—a single migration task supports up to 1,000 tables. If you exceed this limit, the task fails with an error when submitted. To fix this, split the tables across multiple tasks or configure a full-database migration task.

    • If you need incremental migration, enable binary logging:

      • Set binlog_format to ROW and binlog_row_image to FULL. Otherwise, the precheck fails and the task cannot start.

        Important

        If your self-managed MySQL source is a dual-master cluster—where each instance acts as both master and slave—enable the log_slave_updates parameter. This ensures DTS can read all binary logs.

      • For RDS for MySQL instances, retain local binary logs for at least three days (seven days recommended). For self-managed MySQL databases, retain local binary logs for at least seven days. If DTS cannot access binary logs, the task fails. In extreme cases, data inconsistency or data loss may occur. Issues caused by binary log retention periods shorter than DTS requires are not covered under the DTS SLA.

        Note

        To set the retention period for local binary logs on an RDS for MySQL instance, see Automatically delete local logs.

    • Operations not allowed on the source database:

      • Do not run DDL operations that change database or table schemas during schema migration or full migration. Otherwise, the migration task fails.

        Note

        During full migration, DTS queries the source database. This creates metadata locks that may block DDL operations on the source database.

      • If you run only full migration, do not write new data to the source instance. Otherwise, source and destination data become inconsistent. To keep data consistent in real time, select schema migration, full migration, and incremental migration.

    • DTS does not migrate data generated by changes that do not write to binary logs. Examples include data restored from physical backups or created by cascade operations.

      Note

      If this occurs, re-run full migration after your business allows it.

    • If your source MySQL database is version 8.0.23 or later and contains invisible hidden columns, DTS cannot read those columns. This may cause data loss.

      Note

      Run ALTER TABLE <table_name> ALTER COLUMN <column_name> SET VISIBLE; to make the hidden column visible. For more information, see Invisible Columns.

    Other limits

    • We recommend using the same MySQL version for source and destination databases to ensure compatibility.

    • If your source database uses temporary-table-mode online DDL operations—including multi-table merge scenarios—or adds function-based indexes to unique key columns, data loss or task failure may occur on the destination database.

    • DTS does not support migrating parsers defined using comment syntax.

    • If a primary key or unique key conflict occurs during migration:

      • If the table schemas are consistent and a record in the destination database has the same primary key value as a record in the source database:

        • During full migration, DTS keeps the record in the destination database. The record from the source database is not migrated.

        • During incremental migration, DTS does not keep the record in the destination database. The record from the source database overwrites the record in the destination database.

      • If the table schemas are inconsistent, only some columns of data may be migrated, or the migration may fail. Proceed with caution.

    • Before migration, assess the performance of both source and destination databases. Run migration during off-peak business hours. Otherwise, full migration consumes read and write resources on both databases and increases database load.

    • Full migration runs INSERT operations concurrently. This fragments destination tables. After full migration, destination tables require more storage space than source tables.

    • If your data includes four-byte characters—such as rare Chinese characters or emojis—the destination database and table must use the utf8mb4 charset.

      Note

      If you use DTS to migrate schemas, set the instance-level parameter character_set_server to utf8mb4 in the destination database.

    • Confirm that DTS migration precision for FLOAT or DOUBLE columns meets your business needs. DTS reads these columns using ROUND(COLUMN,PRECISION). If no precision is defined, DTS uses 38 digits for FLOAT and 308 digits for DOUBLE.

    • DTS tries to recover failed tasks within seven days. Before switching traffic to the destination instance, end or release the task. Or run the revoke command to remove DTS’s write permission on the destination instance account. This prevents automatic recovery from overwriting destination data with source data.

    • DTS does not support converting datetime data to varchar.

    • If DDL writes fail on the destination database, the DTS task continues running. Check the failed DDL statements in the task logs. For instructions, see View task logs.

    • If your RDS for MySQL instance has Always-Encrypted enabled, full migration is not supported.

      Note

      RDS for MySQL instances with Transparent Data Encryption (TDE) enabled support schema migration, full migration, and incremental migration.

    • To migrate database accounts from the source, meet the required prerequisites and review related considerations. For more information, see Migrate database accounts.

    • If a task fails, DTS support staff will attempt to restore it within eight hours. During restoration, they may restart the task or adjust its parameters.

      Note

      Only DTS task parameters are modified—not database parameters. Parameters that may be adjusted include those listed in Modify instance parameters.

    Special cases

    • For self-managed MySQL sources:

      • A master–standby switchover on the source database causes the migration task to fail.

      • DTS calculates latency by comparing the timestamp of the last record migrated to the destination database with the current time. If no DML operations run on the source for a long time, latency reporting becomes inaccurate. If latency appears too high, run a DML operation on the source to update the latency value.

        Note

        If you select full-database migration, create a heartbeat table. Update or write to it every second.

      • DTS periodically runs CREATE DATABASE IF NOT EXISTS `test` on the source database to advance the binary log offset.

      • If your source is Amazon Aurora MySQL or another clustered MySQL instance, ensure the domain name or IP address configured for the task—and its DNS resolution—always points to a read–write (RW) node. Otherwise, the migration task may fail.

    • For RDS for MySQL sources:

      • If you need incremental migration, RDS for MySQL instances that do not record transaction logs—such as RDS for MySQL 5.6 read-only instances—are not supported as sources.

      • DTS periodically runs CREATE DATABASE IF NOT EXISTS `test` on the source database to advance the binary log offset.

    • When the destination database is PolarDB MySQL Edition:

      • DTS automatically creates a database in PolarDB for MySQL. If the name of the database to be migrated does not meet the naming conventions of PolarDB for MySQL, you must create the database in PolarDB for MySQL before you configure the migration task. For related operations, see Manage databases.

      • You cannot adjust the full migration rate.

    Pricing

    Migration typeLink configuration feeData transfer cost
    Schema migration and full migrationFree.Data transfer out of Alibaba Cloud over the public network incurs charges. For details, see Billing overview.
    Incremental migrationCharged. For details, see Billing overview.

    Migration types

    • Schema migration

      Data Transmission Service (DTS) migrates the schema definitions of the migration objects from the source database to the destination database.

      • DTS supports schema migration for tables, views, triggers, stored procedures, and functions.

        Note

        The routine_body of stored procedures, the routine_body of functions, and the select_statement of views are not modified.

      • During schema migration, DTS changes the `DEFINER` to `INVOKER` for the views, stored procedures, and functions to be migrated. This action changes the value of `SQL SECURITY` to `INVOKER`. DTS also sets the `DEFINER` to the destination database account that is used for the migration task.

        Note

        The security authentication method and definer of the source database are not modified.

      • Because DTS does not migrate user information, you must grant read and write permissions to the invoker to call views, stored procedures, and functions in the destination database.

    • Full migration

      DTS migrates all historical data of the specified migration objects from the source database to the destination database.

    • Incremental migration

      After a full migration is complete, DTS migrates incremental data updates from the source database to the destination database. Incremental migration lets you smoothly migrate data without interrupting your self-managed applications.

    SQL operations supported for incremental migration

    Operation type

    SQL statement

    DML

    INSERT, UPDATE, DELETE

    DDL

    • ALTER TABLE, ALTER VIEW

    • CREATE FUNCTION, CREATE INDEX, CREATE PROCEDURE, CREATE TABLE, CREATE VIEW

    • DROP INDEX, DROP TABLE

    • RENAME TABLE

      Important

      A RENAME TABLE operation may cause data inconsistency. For example, if you select only one table as the migration object and rename the table in the source instance during migration, the data of this table is not migrated to the destination database. To prevent this issue, select the entire database to which the table belongs as the migration object when you configure the data migration task. Make sure that the databases to which the table belongs before and after the RENAME TABLE operation are both included in the migration objects.

    • TRUNCATE TABLE

    Database account permissions

    Database

    Schema migration

    Full migration

    Incremental migration

    Self-managed MySQL database

    SELECT permission

    SELECT permission

    SELECT permission on objects to migrate

    REPLICATION CLIENT, REPLICATION SLAVE, and SHOW VIEW permissions

    Permissions to create databases and tables, so DTS can create the dts database to store heartbeat data

    PolarDB for MySQL cluster

    Read and write permission

    To create and authorize database accounts, perform the following steps:

    Procedure

    1. Navigate to the migration task list page for the destination region using one of the following methods.

      From the DTS console

      1. Log on to the Data Transmission Service (DTS) console.

      2. In the navigation pane on the left, click Data Migration.

      3. In the upper-left corner of the page, select the region where the migration instance is located.

      From the DMS console

      Note

      The actual operations may vary based on the mode and layout of the DMS console. For more information, see Simple mode console and Customize the layout and style of the DMS console.

      1. Log on to the Data Management (DMS) console.

      2. In the top menu bar, choose Data + AI > Data Transmission (DTS) > Data Migration.

      3. To the right of Data Migration Tasks, select the region where the migration instance is located.

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

    3. Optional: In the upper-right corner of the page, click New Configuration Page.

      Note

      • If you are already on the new configuration page (the button in the upper-right corner is Back to Previous Version), you can skip this step.

      • The parameters on the new and old configuration pages are different. We recommend that you use the new configuration page.

    4. Configure the source and destination databases.

      Warning

      After you select the source and destination instances, we recommend that you carefully read the limits displayed at the top of the page. Otherwise, the task may fail or data inconsistency may occur.

      Category

      Configuration

      Description

      None

      Task Name

      DTS automatically generates a task name. We recommend that you specify a descriptive name for easy identification. The name does not need to be unique.

      Source Database

      Select Existing Connection

      • To use a database instance that has been added to the system (created or saved), select the desired database instance from the drop-down list. The database information below will be automatically configured.

        Note

        In the DMS console, this parameter is named Select a DMS database instance..

      • If you have not registered the database instance with the system, or do not need to use a registered instance, manually configure the database information below.

      Database Type

      Select MySQL.

      Connection Type

      Select based on where your source database is deployed. This topic uses Public IP Address as an example.

      Note

      If your self-managed database is another instance type, complete additional preparations. For details, see Preparations overview.

      Instance Region

      Select the region where your self-managed MySQL database resides.

      Note

      Select a region physically close to your self-managed MySQL database—even if it is not hosted in the cloud—to ensure optimal network performance and access speed.

      Hostname or IP address

      Enter the endpoint of your self-managed MySQL database. In this example, enter the public IP address.

      Port

      Enter the service port of your self-managed MySQL database (must be open to the public network). Default is 3306.

      Database Account

      Enter the account for your self-managed MySQL database. For required permissions, see Database account permissions.

      Database Password

      Enter the password for the database account.

      Encryption

      Select Non-encrypted or SSL-encrypted as needed.

      • If SSL encryption is not enabled for the self-managed MySQL database, select Non-encrypted.

      • If SSL encryption is enabled for the self-managed MySQL database, select SSL-encrypted. You also need to upload a CA Certificate and enter the CA Key.

      Destination Database

      Select Existing Connection

      • To use a database instance that has been added to the system (created or saved), select the desired database instance from the drop-down list. The database information below will be automatically configured.

        Note

        In the DMS console, this parameter is named Select a DMS database instance..

      • If you have not registered the database instance with the system, or do not need to use a registered instance, manually configure the database information below.

      Database Type

      Select PolarDB for MySQL.

      Connection Type

      Select Cloud instance.

      Instance Region

      Select the region where your destination PolarDB for MySQL cluster resides.

      PolarDB instance ID

      Select the ID of your destination PolarDB for MySQL cluster.

      Database Account

      Enter the database account for your destination PolarDB for MySQL cluster. For required permissions, see Database account permissions.

      Database Password

      Enter the password for the database account.

      Encryption

      Select an option based on your business requirements. For more information about SSL encryption, see Configure SSL encryption.

    5. After you complete the configuration, click Test Connectivity and Proceed at the bottom of the page. In the CIDR Blocks of DTS Servers dialog box that appears, click Test Connectivity.

      Note

      Ensure that the IP address segments of the DTS service are 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 DTS server IP addresses to a whitelist.

    6. Configure the task objects.

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

        Configuration

        Description

        Migration Types

        • If you only need to perform a full migration, select both Schema Migration and Full Data Migration.

        • To perform a migration with no downtime, select Schema Migration, Full Data Migration, and Incremental Data Migration.

        Note

        • If you do not select Schema Migration, you must ensure that a database and tables to receive the data exist in the destination database. You can also use the object name mapping feature in the Selected Objects box as needed.

        • If you do not select Incremental Data Migration, do not write new data to the source instance during data migration to ensure data consistency.

        Method to Migrate Triggers in Source Database

        Select a trigger migration method as needed. You can skip this step if the objects to be migrated do not include triggers. For more information, see Configure a trigger migration method.

        Note

        You can configure this parameter only if Migration Types includes Schema Migration.

        Processing Mode of Conflicting Tables

        • Precheck and Report Errors: Checks whether tables with the same names exist in the destination database. If no tables with the same names exist, the precheck is passed. If tables with the same names exist, an error is reported during the precheck, and the data migration task does not start.

          Note

          If a table in the destination database has the same name but cannot be easily deleted or renamed, you can change the name of the table in the destination database. For more information, see Object name mapping.

        • Ignore Errors and Proceed: Skips the check for tables with the same names.

          Warning

          Selecting Ignore Errors and Proceed may cause data inconsistency and business risks. For example:

          • If the table schemas are consistent and a record in the destination database has the same primary key value as a record in the source database:

            • During full migration, DTS keeps the record in the destination database. The record from the source database is not migrated.

            • During incremental migration, DTS does not keep the record in the destination database. The record from the source database overwrites the record in the destination database.

          • If the table schemas are inconsistent, only some columns of data may be migrated, or the migration may fail. Proceed with caution.

        Whether to migrate Event

        Select whether to migrate events from the source database. If you select Yes, you must meet specific requirements and perform additional steps. For more information, see Migrate or synchronize events.

        Capitalization of Object Names in Destination Instance

        You can configure the case sensitivity policy for the names of migrated objects, such as databases, tables, and columns, in the destination instance. By default, DTS default policy is selected. You can also choose to keep the case sensitivity consistent with the default policy of the source or destination database. For more information, see Case sensitivity of object names in the destination database.

        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

        The granularity for selecting migration objects is schema, table, and column. If you select only tables or columns as migration objects, other objects such as views, triggers, and stored procedures are not migrated to the destination database.

        Selected Objects
        Note

        • Using object name mapping may cause the migration of dependent objects to fail.

        • To filter data using a WHERE clause, right-click a table in the Selected Objects box and set the filter condition in the dialog box that appears. For more information, see Set filter conditions.

        • To select SQL operations at the database or table level, right-click an object in the Selected Objects box and select the required SQL operations in the dialog box that appears. For information about the supported operations, see SQL operations supported for incremental migration.

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

        Configuration

        Description

        Dedicated Cluster for Task Scheduling

        By default, DTS schedules tasks on a shared cluster. You do not need to select one. If you want more stable tasks, you can purchase a dedicated cluster to run DTS migration tasks.

        Select the engine type of the destination database

        Select the engine type for the destination database.

        • InnoDB: the default storage engine.

        • X-Engine: an online transaction processing (OLTP) database storage engine.

        Copy the temporary table of the Online DDL tool that is generated in the source table to the destination database.

        If you use Data Management (DMS) or gh-ost to perform online DDL changes in the source database, you can choose whether to migrate the data from the temporary tables generated by the online DDL changes.

        Important

        • DTS tasks do not support using tools such as pt-online-schema-change to perform online DDL changes. Otherwise, the DTS task fails.

        • The processing methods for each phase are as follows: The Schema Migration and Full Data Migration phases do not allow DDL operations that change the database or table structure. Therefore, they are not controlled by the online DDL policy.

          • Schema Migration: Not controlled by the online DDL policy. Related temporary tables are created.

          • Full Data Migration: Not controlled by the online DDL policy. The migration of temporary tables is not included in the full migration objects. All tables whose names match the regular expression (^_(.+)_(?:gho|new)$ or ^_(.+)_(?:ghc|del|old)$) are filtered out.

          • Incremental Data Migration: Controlled by the online DDL policy.

            • Yes: Migrates data changes from temporary tables (for example, _table_name_gho) generated by online DDL operations.

            • No, Adapt to DMS Online DDL and No, Adapt to gh-ost: Filters out data changes from temporary tables (for example, _table_name_gho) generated by tools such as gh-ost based on regular expression rules.

        • Yes: Migrates the data from the temporary tables generated by online DDL changes.

          Note

          If online DDL changes generate a large amount of data in temporary tables, it may cause task latency.

        • No, Adapt to DMS Online DDL: Does not migrate the data from the temporary tables generated by online DDL changes. It only migrates the original DDL statements executed using Data Management (DMS).

          Note

          This option causes tables in the destination database to be locked.

        • No, Adapt to gh-ost: Does not migrate the data from the temporary tables generated by online DDL changes. It supports custom filtering rules. DTS filters out data changes from temporary tables (for example, _table_name_gho) generated by tools such as gh-ost based on regular expression rules. You can modify the default regular expressions used to match shadow and useless tables as needed:

          • Shadow table: ^_(.+)_(?:gho|new)$

          • Useless table: ^_(.+)_(?:ghc|del|old)$

          Note

          This option causes tables in the destination database to be locked.

        Whether to Migrate Accounts

        Select whether to migrate account information from the source database. If you select Yes, select the accounts to migrate and confirm their permissions.

        Retry Time for Failed Connections

        After the migration task starts, if the connection to the source or destination database fails, DTS reports an error and immediately begins to retry the connection. The default retry duration is 720 minutes. You can customize the retry time to a value from 10 to 1440 minutes. We recommend that you set the duration to more than 30 minutes. If DTS reconnects to the source and destination databases within the specified duration, the migration task automatically resumes. Otherwise, the task fails.

        Note

        • For multiple DTS instances that share the same source or destination, the network retry time is determined by the setting of the last created task.

        • Because you are charged for the task during the connection retry period, we recommend that you customize the retry time based on your business needs, or release the DTS instance as soon as possible after the source and destination database instances are released.

        Retry Time for Other Issues

        After the migration task starts, if a non-connectivity issue, such as a DDL or DML execution exception, occurs in the source or destination database, DTS reports an error and immediately begins to retry the operation. The default retry duration is 10 minutes. You can customize the retry time to a value from 1 to 1440 minutes. We recommend that you set the duration to more than 10 minutes. If the related operations succeed within the specified retry duration, the migration task automatically resumes. Otherwise, the task fails.

        Important

        The value of Retry Time for Other Issues must be less than the value of Retry Time for Failed Connections.

        Enable Throttling for Full Data Migration

        During full migration, DTS consumes read and write resources on the source and destination databases, which may increase the database load. If required, you can enable throttling for the full migration task. You can set Queries per second (QPS) to the source database, RPS of Full Data Migration, and Data migration speed for full migration (MB/s) to reduce the load on the destination database.

        Note

        • This configuration item is available only if you select Full Data Migration for Migration Types.

        • You can also adjust the full migration speed after the migration instance is running.

        Enable Throttling for Incremental Data Migration

        If required, you can also choose to set speed limits for the incremental migration task. You can set RPS of Incremental Data Migration and Data migration speed for incremental migration (MB/s) to reduce the load on the destination database.

        Note

        • This configuration item is available only if you select Incremental Data Migration for Migration Types.

        • You can also adjust the incremental migration speed after the migration instance is running.

        Environment Tag

        Select an environment tag to identify the instance. For this example, you do not need to select a tag.

        Whether to delete SQL operations on heartbeat tables of forward and reverse tasks

        Choose whether DTS writes heartbeat SQL information to the source database while the instance is running.

        • Yes: Does not write heartbeat SQL information to the source database. The DTS instance may display latency.

        • No: Writes heartbeat SQL information to the source database. This may interfere with source database operations like physical backups and cloning.

        Configure ETL

        Choose whether to enable the extract, transform, and load (ETL) feature. For more information, see What is ETL? Valid values:

        Monitoring and Alerting

        Select whether to set alerts and receive alert notifications based on your business needs.

        • No: Does not set an alert.

        • Yes: Configure alerts by setting an alert threshold and an alert notifications. If a migration fails or the latency exceeds the threshold, the system sends an alert notification.

      3. Click Next: Data Validation to configure a data validation task.

        For more information about the data validation feature, see Configure data validation.

    7. Save the task and run a precheck.

      • To view the parameters for configuring this instance when you call the API operation, move the pointer over the Next: Save Task Settings and Precheck button and click Preview OpenAPI parameters in the bubble that appears.

      • If you do not need to view or have finished viewing the API parameters, click Next: Save Task Settings and Precheck at the bottom of the page.

      Note

      • Before the migration task starts, DTS performs a precheck. The task starts only after it passes the precheck.

      • If the precheck fails, click View Details next to the failed check item, fix the issue based on the prompt, and then run the precheck again.

      • If a warning is reported during the precheck:

        • For check items that cannot be ignored, click View Details next to the failed item, fix the issue based on the prompt, and then run the precheck again.

        • For check items that can be ignored, you can click Confirm Alert Details, Ignore, OK, and Precheck Again to skip the alert item and run the precheck again. If you choose to ignore a warning, it may cause issues such as data inconsistency and pose risks to your business.

    8. Purchase the instance.

      1. When the Success Rate is 100%, click Next: Purchase Instance.

      2. On the Purchase page, select the link specification for the data migration instance. For more information, see the following table.

        Category

        Parameter

        Description

        New Instance Class

        Resource Group Settings

        Select the resource group to which the instance belongs. The default value is default resource group. For more information, see What is Resource Management?

        Instance Class

        DTS provides migration specifications with different performance levels. The link specification affects the migration speed. You can select a specification based on your business scenario. For more information, see Data migration link specifications.

      3. After the configuration is complete, read and select Data Transmission Service (Pay-as-you-go) Service Terms.

      4. Click Buy and Start. In the OK dialog box that appears, click OK.

        You can view the progress of the migration task on the Data Migration Tasks list page.

        Note

        • If the migration task does not include incremental migration, it stops automatically after the full migration is complete. After the task stops, its Status changes to Completed.

        • If the migration task includes incremental migration, it does not stop automatically. The incremental migration task continues to run. While the incremental migration task is running, the Status of the task is Running.