This topic describes how to migrate data from an Apsara PolarDB for MySQL cluster to a user-created 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 for the Apsara PolarDB for MySQL cluster is enabled. For more information, see Enable binary logging.

Precautions

  • DTS uses read and write resources of the source and destination databases during full data migration. This may increase the database load. 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 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 usage 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. Before a user can call views, stored procedures, and functions of the destination database, you must grant the read/write permissions to the user.

Migration types

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

Billing

Migration type Instance configuration Internet traffic
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 type SQL statement
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

Database Permission
Apsara PolarDB for MySQL cluster The read permission for the objects to be migrated
User-created MySQL database The read/write permissions for 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 an RDS for MySQL instance.

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
    Section Parameter Description
    N/A Task Name DTS automatically generates a task name. We recommend that you use 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 for the source PolarDB cluster. For more information about permissions required for the account, see #section_9df_6td_ufp.
    Database Password Enter the password for the database account.
    Note After you specify the source database parameters, click Test Connectivity next to the Database Password parameter 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 User-Created Database in ECS Instance.
    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 user-created MySQL database.
    Database Type Select MySQL.
    Port Number Enter the service port number of the user-created MySQL database. In this example, enter 3306.
    Database Account Enter the account for the user-created MySQL database. For more information about permissions required for the database account, see #section_9df_6td_ufp.
    Database Password Enter the password for the database account.
    Note After you specify the destination database parameters, click Test Connectivity next to the Database Password parameter to verify whether the 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. Click Set Whitelist and Next in the lower-right corner of the page.
    Note The CIDR blocks of DTS servers are automatically added 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 destination instance.
  7. Select the migration types and objects to be migrated.
    Select the migration types and objects to be migrated
    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 Incremental Data Migration is not selected, do not write data to the source database during full data migration. This ensures data consistency between the source and destination databases.
    Objects

    Select objects from the Available section and click the Right arrow icon to move the objects to the Selected section.

    Note
    • You can select columns, tables, or databases as the objects to be migrated.
    • After an object is migrated to the destination database, the name of the object remains unchanged. You can change the names of the objects that are migrated to the destination database by using the object name mapping feature. For more information about how to use this feature, see Object name mapping.
    • If you use the object name mapping feature on an object, other objects that are dependent on the object may fail to be migrated.
  8. In the lower-right corner of the page, click Precheck.
    Notice
    • Before you can start the data migration task, a precheck is performed. A data migration task can be started only if it passes the precheck.
    • If the task fails to pass the precheck, click the Info icon icon next to each failed item to view details. Troubleshoot the issues based on the causes and perform 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 a data migration task. Otherwise, data migrated to the destination database will be incomplete. Wait until the data migration task automatically stops.

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

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

      Notice Select an appropriate time to manually stop the migration task. For example, you can stop the migration task during off-peak hours or before you switch your workloads to the destination instance.
      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. After the status of incremental data migration changes to The migration task is not delayed, manually stop the migration task.Stop an incremental data migration task