Migrate data from an ApsaraDB for PolarDB database to an ApsaraDB RDS for MySQL database

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

Billing

SQL operations that can be synchronized during incremental data migration

Permissions required for 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 RDS instance resides.
   
4. In the upper-right corner of the page, click Create Migration Task.
5. 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 ApsaraDB for PolarDB cluster ID.
   	Database Account	Enter the ApsaraDB for PolarDB database account. For more information about the permissions required for the ApsaraDB for PolarDB database account, see Permissions required for database accounts.
   	Database Password	Enter the password of the ApsaraDB for PolarDB database account. Note After you specify the source database parameters, click Test Connectivity next to the Database Password parameter to verify whether the parameters are valid. If the source database parameters are valid, 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 RDS Instance.
   	Instance Region	Select the region where the RDS instance resides.
   	Database Account	Enter the ApsaraDB RDS for MySQL database account. For more information about the permissions required for the ApsaraDB RDS for MySQL database account, see Permissions required for database accounts.
   	Database Password	Enter the password of the ApsaraDB RDS for MySQL 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 destination database parameters are valid, 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.
   	Encryption	Select Non-encrypted or SSL-encrypted as needed. If you select SSL-encrypted, you must enable the SSL encryption feature for the RDS instance. For more information about how to enable the feature, see Configure SSL encryption for a RDS instance. Note Encryption is available only in mainland China and Hong Kong(China).

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 ApsaraDB for PolarDB cluster and RDS instance. This makes sure that DTS servers can connect to the PolarDB cluster and RDS instance.
7. 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 icon 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, 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 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.
12. Switch your workloads to the RDS instance.