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.

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.
  • Concurrent insertions are performed during full data migration. This results in table fragmentation in the destination instance. After a full data migration task is completed, the tablespace of the destination instance is larger than that of the source instance.
  • 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.

Limits

  • DTS supports schema migration of the following objects: tables, views, triggers, stored procedures, and stored functions.
    Note During schema migration, the DEFINER mode of views, stored procedures, and stored functions is shifted to the INVOKER mode.
  • The information of the source database account cannot be migrated. If you need to use views, stored procedures, and stored functions, you must grant read and write permissions to the destination database account.

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 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 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 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 Permissions required for database accounts.
    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 Permissions required for database accounts.
    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. 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 disruptions to your business, 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 > to move them to the Selected section.

    Note
    • Objects to be migrated can be databases, tables, or columns.
    • The selected objects are not renamed after the migration by default. If you want to rename the objects 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 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