Migrate data between PolarDB for MySQL clusters

Prerequisites

• The source and destination PolarDB for MySQL clusters are created. For more information, see Create a PolarDB for MySQL cluster.

• To perform an incremental data migration, the source PolarDB for MySQL cluster must have binary logging enabled. For more information, see Enable binary logging.

Usage notes

• During a full data migration, DTS consumes read and write resources on the source and destination databases, increasing their load. If your databases have poor performance, low specifications, or high workloads (for example, if the source database has many slow SQL queries or tables without primary keys, or if deadlocks occur in the destination database), the increased load can strain your databases or even cause service interruptions. Perform the data migration during off-peak hours, such as when the CPU utilization of both databases is below 30%.

• If the source database contains tables without primary keys or unique constraints, and the columns are not unique, duplicate data may appear in the destination database.

• If a migration task fails, DTS automatically attempts to resume it. Before you switch your business to the destination database, you must stop or release the task. This prevents the resumed task from overwriting destination data with source data.

Migration types

Billing

SQL operations for incremental migration

Required permissions for database accounts

Procedure

1. Log on to the DTS console.

   Note

   If you are automatically redirected to the Data Management (DMS) console, you can click the icon in the lower-right corner and then click to return to the classic DTS console.

2. In the left-side navigation pane, click Data Migration.

3. At the top of the Migration Tasks page, select the region of the destination cluster.

4. In the upper-right corner of the page, click Create Data Migration Task.

5. Configure the connection settings for the source and destination databases.

   Section	Parameter	Description
   N/A	Task name	DTS automatically generates a task name. We recommend using a descriptive name for easy identification. The name does not need to be unique.
   Source database	Instance type	Select PolarDB.
   	Instance region	Select the region of the source PolarDB for MySQL cluster.
   	PolarDB instance ID	Select the ID of the source PolarDB for MySQL cluster.
   	Database account	Enter the database account used to connect to the source PolarDB for MySQL cluster.
   	Database password	Enter the password for the database account. Note After configuring the source database, click Test Connectivity next to Database Password to verify that the information is correct. If the connection test is successful, a Passed message appears. If the test fails with a Failed message, click Diagnose next to the Failed message and modify the source database settings as prompted.
   Destination database	Instance type	Select PolarDB.
   	Instance region	Select the region of the destination PolarDB for MySQL cluster.
   	PolarDB instance ID	Select the ID of the destination PolarDB for MySQL cluster.
   	Database account	Enter the database account of the destination PolarDB for MySQL cluster.
   	Database password	Enter the password for the database account. Note After configuring the destination database, click Test Connectivity next to Database Password to verify that the information is correct. If the connection test is successful, a Passed message appears. If the test fails with a Failed message, click Diagnose next to the Failed message and modify the destination database settings as prompted.

6. After you complete the configurations, click Set Whitelist and Next in the lower-right corner of the page.

   For Alibaba Cloud database instances like ApsaraDB RDS for MySQL or ApsaraDB for MongoDB, DTS automatically adds its server CIDR blocks to the instance's whitelist. For a database self-hosted on an ECS instance, DTS adds the CIDR blocks to the security group rules automatically. For clusters on multiple ECS instances, or for databases in an on-premises data center or on a third-party cloud, you must manually add the CIDR blocks to allow access. For a list of required CIDR blocks, see CIDR blocks of DTS servers.

   Warning

   Adding the public CIDR blocks of DTS servers, whether automatically or manually, may introduce security risks. By using this product, you acknowledge and accept these potential risks. You are responsible for implementing basic security measures, including but not limited to using strong passwords, restricting open ports, using authentication for internal API calls, regularly reviewing and restricting unnecessary network segments, or connecting through private networks such as Express Connect, VPN Gateway, or Smart Access Gateway.

7. Select the migration types and objects.

   Setting	Description
   Migration types	To perform only a full migration, select both Schema Migration and Full Data Migration. To perform a zero-downtime migration, select Schema Migration, Full Data Migration, and Incremental Data Migration. Important If you do not select Incremental Data Migration, do not write new data to the source database during the full data migration to ensure data consistency.
   Migration objects	In the Available box, click the objects that you want to migrate and click the icon to move them to the Selected Objects box. Important You can select objects to migrate at the database, table, and column levels. By default, object names are retained after migration. If you need to rename an object in the destination database, use the object name mapping feature. For more information, see Object name mapping. If you rename an object by using the object name mapping feature, other objects that depend on it may fail to migrate.
   Object name mapping	If you need to rename a migrated object in the destination instance, use the object name mapping feature. For more information, see Object name mapping.
   Connection retry duration	If a connection to the source or destination database is interrupted, DTS retries to connect for a default of 720 minutes (12 hours). You can customize this duration. If DTS successfully reconnects within the specified time, the migration task resumes. Otherwise, the task fails. Note You are charged for the DTS instance while it attempts to reconnect. To avoid unnecessary charges, set an appropriate retry duration or release the DTS instance promptly if the source and destination databases are released.
   Replicate temporary tables created during online DDL operations in DMS	If you use Data Management (DMS) to perform online DDL operations on the source database, you can choose whether to migrate the temporary tables that are generated. Yes: Migrates the data in the temporary tables that are generated by online DDL operations. Note If a large amount of temporary table data is generated by online DDL operations, the migration task may experience high latency. No: Does not migrate the data in the temporary tables. Only the original DDL data from the source database is migrated. Note This option may cause table locks on the destination database.

8. After you complete the configuration, click Precheck and Start in the lower-right corner of the page.

   Note

   • Before the migration task starts, DTS runs a precheck. The task can start only after it passes the precheck.

   • If the precheck fails, click the icon next to the failed item to view details.

     • Fix the issues as prompted and run the precheck again.

     • If you do not need to fix the warning items, you can select Ignore and then click Ignore Warnings and Rerun Precheck to run the precheck again.

9. After the task passes the precheck, click Next.

10. In the Confirm Settings dialog box that appears, select a Instance Class and select the Data Transmission Service (pay-as-you-go) Service Terms checkbox.

11. Click Buy and Start to begin the migration.

    • Schema migration + Full data migration

      Allow the task to complete automatically. Stopping it manually may result in incomplete data.

    • Schema migration + Full data migration + Incremental data migration

      The migration task does not stop automatically. You must stop it manually.

      Important

      Choose an appropriate time to stop the task manually, such as during off-peak hours or when you are ready to switch your business to the destination cluster.

      1. Wait until the migration task enters the Incremental Data Migration phase and the status shows Undelayed. Then, stop writing data to the source database for several minutes. During this time, the status of Incremental Data Migration may show a latency.

      2. Wait for the Incremental Data Migration status to show Undelayed again. Then, manually stop the migration task. Select the check box of the target migration task, and click Pause in the batch operation bar at the bottom of the page.

12. Switch your business to the PolarDB for MySQL cluster.