ApsaraDB for PolarDB is a next-generation relational database service developed by Alibaba Cloud. It is a high-performance, high-availability, easy-to-use, and reliable service that is compatible with the MySQL database engine. You can use Data Transmission Service (DTS) to migrate data between ApsaraDB for PolarDB clusters.

Prerequisites

Background information

  • 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%.
  • If your ApsaraDB RDS for MySQL database does not have primary key or unique constraints and each field in the database has duplicate values, the data migrated to the destination database may be duplicated.
  • If a data migration task fails, DTS attempts to resume the task. In this case, before you switch your workloads to the destination database, you must stop or release the task. Otherwise, the data in the source database will overwrite the data in the destination database after the task is resumed.

Migration types

DTS supports schema migration, full data migration, and incremental data migration. For more information, see Terms.
Note You can use these three migration types together to migrate data without service interruptions.

Billing

Migration type Migration channel fee Public network traffic fee
Schema migration or full data migration Free of charge Migrating data from Alibaba Cloud over the Internet incurs fees. For more information, see Pricing.
Incremental data migration Billed. For more information, see Pricing.

SQL operations that can be synchronized during incremental data migration

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

Database Required permissions
Source ApsaraDB for PolarDB cluster Read permission on objects to be migrated
Destination ApsaraDB for PolarDB cluster Read and write permissions on migrated objects
Note For more information about how to create and authorize a database account, see Create an ApsaraDB RDS for MySQL database account.

Procedure

  1. Log on to the DTS console.
  2. In the left-side navigation pane, click Data Migration.
  3. At the top of Migration Tasks the 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 Source and Destination Databases
    Section Parameter Description
    N/A Task Name DTS generates a random task name. However, we recommend that you specify an informative name to ease management.
    Source Database Instance Type Select PolarDB.
    Instance Region Select the region where the source ApsaraDB for PolarDB cluster resides.
    PolarDB Instance ID Select the source ApsaraDB for PolarDB cluster ID.
    Database Account Enter the database account of the source ApsaraDB for PolarDB cluster.
    Database Password Enter the password of the database account.
    Note After the source database parameters are specified, click Test Connectivity next to the Database Password parameters to verify whether the specified parameters are correct. If the source database parameters are correct, the Test Passed message is displayed. If the Test Failed message is displayed, click Diagnose in the Test Failed message. Modify the source database parameters as prompted.
    Destination Database Instance Type Select PolarDB.
    Instance Region Select the region where the destination ApsaraDB for PolarDB cluster resides.
    PolarDB Instance ID Enter the destination ApsaraDB for PolarDB cluster ID.
    Database Account Enter the database account of the destination ApsaraDB for PolarDB cluster.
    Database Password Enter the password of the database account.
    Note After the destination database parameters are specified, click Test Connectivity next to the Database Password parameter to verify whether the specified parameters are correct. If the destination database parameters are correct, the Test Passed message is displayed. If the Test Failed message is displayed, click Diagnose in the Test Failed message. Modify the destination database parameters as prompted.
  6. Click Set Whitelist and Next in the lower-right corner of the page.
    Note The IP addresses of DTS servers are added to the whitelist of the source and destination ApsaraDB for PolarDB clusters. This makes sure that the DTS server can connect to the clusters.
  7. Configure migration types and objects.
    Configure Migration Types and Objects
    Item Description
    Migration types
    • To perform only full data migration, select Schema Migration and Full Data Migration.
    • If you want to migrate data without business disruptions, select Schema Migration, Full Data Migration, and Incremental Data Migration.
    Note If Incremental Data Migration is not selected, do not write data into the source database during full data migration. This ensures data consistency between the source and destination databases.
    Objects to be migrated

    Select the objects to be migrated in the Available section and click > icon to move them to the Selected section.

    Note
    • Objects to be migrated can be databases, tables, or columns.
    • By default, the selected objects are not renamed after the migration. If you want to rename the objects that are migrated to the destination instance, you can use the object name mapping feature provided by DTS. For more information about how to use this feature, see Object name mapping.
    • If you use the object name mapping feature for an object, objects that depend on the object may fail to be migrated.
  8. Click Precheck on the lower right of the page.
    Note
    • A precheck is performed for a data migration task. A data migration task can be started only if it passes the precheck.
    • If the precheck fails, click Note icon corresponding to each failed item to view the details. Fix the problems as instructed and run the precheck again.
  9. After the precheck is passed, click Next.
  10. On the Confirm Settings dialog box that appears, specify Channel Specification and select the 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

      Do not manually stop a migration task. Otherwise, data migrated to the destination database will be incomplete. Wait until the data migration task stops when it is complete.

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

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

      Note Select an appropriate time point to manually end the migration task. For example, you can end the migration task during off-peak hours or before you switch your workloads to the destination cluster.
      1. When the task progress bar switches to Incremental Data Migration and the message The migration task is not delayed appears, stop writing new data to the source database for a few minutes. Then, the progress bar will show the latency of the incremental data migration.
      2. When the status of incremental data migration changes to The migration task is not delayed, manually stop the migration task.Stop the incremental migration task
  12. Switch your workloads to the destination cluster.

What to do next

After the data migration is complete, you must delete the accounts of both the source and destination databases to ensure security.