This topic describes how to migrate data from a PolarDB for MySQL cluster to a self-managed MySQL database by using Data Transmission Service (DTS). This is applicable to scenarios such as data analysis and functional test.

Prerequisites

The binary logging feature is enabled for the source PolarDB for MySQL cluster. For more information, see Enable binlogging.

Precautions

  • DTS uses read and write resources of the source and destination databases during full data migration. This may increase the loads of the database servers. If the database performance is unfavorable, the specification is low, or the data volume is large, database services may become unavailable. For example, DTS occupies a large amount of read and write resources in the following cases: a large number of slow SQL queries are performed on the source database, the tables have no primary keys, or a deadlock occurs in the destination database. 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. For example, you can migrate data when the CPU utilization of the source and destination databases is less than 30%.
  • The source database must have PRIMARY KEY or UNIQUE constraints and all fields must be unique. Otherwise, the destination database may contain duplicate data records.
  • During full data migration, concurrent INSERT operations cause fragmentation in the tables of the destination database. After full data migration is complete, the tablespace of the destination database is larger than that of the source database.
  • If a data migration task fails, DTS automatically resumes the task. Before you switch your workloads to the destination database, stop or release the data migration task. Otherwise, the data in the source database will overwrite the data in the destination database after the task is resumed.

Limits

  • DTS supports schema migration for the following types of objects: table, view, trigger, stored procedure, and function.
    Note
    During schema migration, DTS changes the value of the SECURITY attribute from DEFINER to INVOKER for views, stored procedures, and functions.
  • DTS does not migrate user information from the source database. After data migration is complete, to call a view, stored procedure, or function of the destination database, you must grant the read and write permissions to INVOKER.

Migration types

DTS supports schema migration, full data migration, and incremental data migration. For more information, see Terms.
Note
When you migrate data between PolarDB for MySQL clusters, you can select all of the supported migration types to ensure service continuity.

Billing

Migration typeTask configuration feeInternet traffic fee
Migration type Task configuration fee Internet traffic fee
Schema migration and full data migration Free of charge. Charged only when data is migrated from Alibaba Cloud over the Internet. For more information, see Pricing.
Incremental data migration Charged. For more information, see Pricing.

SQL operations that can be synchronized during incremental data migration

Operation typeSQL statements
Operation type SQL statements
DML INSERT, UPDATE, DELETE, and REPLACE
DDL
  • ALTER TABLE and ALTER VIEW
  • CREATE FUNCTION, CREATE INDEX, CREATE PROCEDURE, CREATE TABLE, and CREATE VIEW
  • DROP INDEX and DROP TABLE
  • RENAME TABLE
  • TRUNCATE TABLE

Permissions required for database accounts

DatabaseRequired permissions
Database Required permissions
PolarDB for MySQL The read permissions on the objects to be migrated
Self-managed MySQL database The read and write permissions on the objects to be migrated

For more information about how to create and authorize a database account, see Create database accounts and Create an account for a self-managed MySQL database and configure binary logging.

Procedure

  1. Log on to the DTS console.
  2. In the left-side navigation pane, click Data Migration.
  3. At the top of the Migration Tasks page, select the region where the destination cluster resides.
    Select a region
  4. In the upper-right corner of the page, click Create Migration Task.
  5. Configure the source and destination databases.
    Configure the source and destination databases
    SectionParameterDescription
    Section Parameter Description
    N/A Task Name DTS automatically generates a task name. We recommend that you specify an informative name for easy identification. You do not need to use a unique task name.
    Source Database Instance Type Select PolarDB.
    Instance Region Select the region where the source PolarDB cluster resides.
    PolarDB Instance ID Select the ID of the source PolarDB cluster.
    Database Account Enter the database account of the source PolarDB cluster. For information about the permissions that are required for the account, see Permissions required for database accounts.
    Database Password Enter the password of the database account.
    Note
    After you specify the source database parameters, click Test Connectivity next to Database Password to verify whether the specified parameters are valid. If the specified parameters are valid, the Passed message appears. If the Failed message appears, click Check next to Failed. Modify the source database parameters based on the check results.
    Destination Database Instance Type Select an instance type based on the deployment of the source database. In this example, select User-Created Database in ECS Instance.
    Note
    If you select other instance types, you must deploy the network environment for the source database. For more information, see Preparation overview.
    Instance Region Select the region where the ECS instance resides.
    ECS Instance ID Select the ID of the ECS instance that is connected to the self-managed MySQL database.
    Database Type Select MySQL.
    Port Number Enter the service port number of the self-managed MySQL database. In this example, enter 3306.
    Database Account Enter the account of the self-managed MySQL database. For information about the permissions that are required for the account, see Permissions required for database accounts.
    Database Password Enter the password of the database account.
    Note
    After you specify the destination database parameters, click Test Connectivity next to Database Password to verify whether the specified parameters are valid. If the specified parameters are valid, the Passed message appears. If the Failed message appears, click Check next to Failed. Modify the destination database parameters based on the check results.
    Encryption Select Non-encrypted or SSL-encrypted. In this example, Non-encrypted is selected.
  6. In the lower-right corner of the page, click Set Whitelist and Next.
    Note
    DTS adds the CIDR blocks of DTS servers to the whitelist of the source PolarDB for MySQL cluster and the inbound rule of the destination ECS instance. This ensures that DTS servers can connect to the source cluster and the destination instance.
  7. Select the migration types and the objects to be migrated.
    Select the migration types and the objects to be migrated
    SettingDescription
    Setting Description
    Select the migration types
    • To perform only full 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 Incremental Data Migration is not selected, 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.
    Select the objects to be migrated

    Select one or more objects from the Available section and click the Rightwards arrow icon to move the objects to the Selected section.

    Note
    • You can select columns, tables, or databases as the objects to be migrated.
    • By default, after an object is migrated to the destination database, the name of the object remains unchanged. You can use the object name mapping feature to rename the objects that are migrated to the destination database. For more information, see Object name mapping.
    • 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.
    Specify whether to rename objects You can use the object name mapping feature to rename the objects that are migrated to the destination instance. For more information, see Object name mapping.
    Specify the retry time for failed connections to the source or destination database By default, if DTS fails to connect to the source or destination database, DTS retries within the next 720 minutes (12 hours). You can specify the retry time based on your needs. If DTS reconnects to the source and destination databases within the specified time, DTS resumes the data migration task. Otherwise, the data migration task fails.
    Note
    When DTS retries a connection, you are charged for the DTS instance. We recommend that you specify the retry time based on your business needs. You can also release the DTS instance at your earliest opportunity after the source and destination instances are released.
    Specify whether to copy temporary tables to the destination database when DMS performs online DDL operations on the source table If you use Data Management (DMS) to perform online DDL operations on the source database, you can specify whether to migrate temporary tables generated by online DDL operations.
    • Yes: DTS migrates the data of temporary tables generated by online DDL operations.
      Note
      If online DDL operations generate a large amount of data, the data migration task may be delayed.
    • No: DTS does not migrate the data of temporary tables generated by online DDL operations. Only the original DDL data of the source database is migrated.
      Note
      If you select No, the tables in the destination database may be locked.
  8. In the lower-right corner of the page, click Precheck.
    Note
    • Before you can start the data migration task, a precheck is performed. You can start the data migration task only after the task passes the precheck.
    • If the task fails to pass the precheck, you can click the Info icon icon next to each failed item to view details.
      • You can troubleshoot the issues based on the causes and run a precheck again.
      • If you do not need to troubleshoot the issues, you can ignore failed items and run a precheck again.
  9. After the task passes the precheck, click Next.
  10. In the Confirm Settings dialog box, specify the Channel Specification parameter and select Data Transmission Service (Pay-As-You-Go) Service Terms.
  11. Click Buy and Start to start the data migration task.
    • Schema migration and full data migration

      We recommend that you do not manually stop the task during full data migration. Otherwise, the data migrated to the destination database will be incomplete. You can wait until the data migration task automatically stops.

    • Schema migration, full data migration, and incremental data migration

      The task does not automatically stop during incremental data migration. You must manually stop the task.

      Notice
      We recommend that you select an appropriate time to manually stop the data migration task. For example, you can stop the task during off-peak hours or before you switch your workloads to the destination cluster.
      1. Wait until Incremental Data Migration and The migration task is not delayed appear in the progress bar of the migration task. Then, stop writing data to the source database for a few minutes. The delay time of incremental data migration may be displayed in the progress bar.
      2. Wait until the status of incremental data migration changes to The migration task is not delayed again. Then, manually stop the migration task. Stop a task during incremental data migration