Apsara PolarDB is a next-generation relational database service that is developed by Alibaba Cloud. The service is compatible with the MySQL database engine and features high availability, ease of use, and reliability. This topic describes how to migrate data between Apsara PolarDB for MySQL clusters by using Data Transmission Service (DTS).

Note PolarDB does not support the major version upgrade. For example, you cannot upgrade PolarDB for MySQL 5.6 to PolarDB for MySQL 8.0 directly. However, you can create a cluster of a later version as the destination cluster, such as PolarDB for MySQL 8.0, and use DTS to migrate data from the source cluster to the destination cluster. Before you migrate data between different versions of Apsara PolarDB for MySQL clusters, we recommend that you create a pay-as-you-go PolarDB cluster to test the compatibility. After testing, you can release the cluster.

Prerequisites

  • The source and destination Apsara PolarDB for MySQL clusters are created. For more information, see Create a PolarDB MySQL cluster.
  • The binary logging feature is enabled for the source Apsara 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 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.
  • 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 from 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 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 Required permission
Source Apsara PolarDB for MySQL cluster The read permission on the objects to be migrated
Destination Apsara PolarDB for MySQL cluster The read/write permissions on the objects to be migrated
Note For more information about how to create and authorize a database account, see Create database accounts.

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 for the data migration task.
    Configure the source and destination databases
    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.
    Database Password Enter the password of the source 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 PolarDB.
    Instance Region Select the region where the destination PolarDB cluster resides.
    PolarDB Instance ID Select the ID of the destination PolarDB cluster.
    Database Account Enter the database account of the destination PolarDB cluster.
    Database Password Enter the password of the destination 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.
  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 whitelists of the source and destination PolarDB clusters. This ensures that DTS servers can connect to the source and destination PolarDB clusters.
  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.
    Notice 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.

    Notice
    • 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
  12. Switch your workloads to the destination PolarDB cluster.

What to do next

The database accounts that are used for data migration have the read/write permissions. After data migration is complete, you must delete the database accounts to ensure security.