PolarDB is a next-generation relational database service that is developed by Alibaba Cloud. PolarDB is compatible with the MySQL database engine and features high availability, ease of use, and reliability. This topic describes how to migrate data between PolarDB for MySQL clusters by using Data Transmission Service (DTS).
Note A PolarDB for MySQL cluster of an earlier version cannot be upgraded to 8.0. However, you can create a PolarDB for MySQL cluster of version 8.0, and then migrate data to this cluster. Before you migrate data between different versions of 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 PolarDB for MySQL clusters are created. For more information, see Create a PolarDB for MySQL cluster.
- The binary logging feature is enabled for the source PolarDB for MySQL cluster. For more information, see Enable binary logging.
Precautions
- DTS uses read and write resources of the source and destination databases during full data migration. This may increase the loads of the database servers. 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 impact of data migration on 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 utilization 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 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 When you migrate data between PolarDB for MySQL clusters, you can select all of the supported migration types to ensure service continuity.
Billing
| Migration type | Task configuration fee | Internet traffic fee |
|---|---|---|
| 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 statements |
|---|---|
| DML | INSERT, UPDATE, DELETE, and REPLACE |
| DDL |
|
Permissions required for database accounts
| Database | Required permissions |
|---|---|
| Source PolarDB for MySQL cluster | The read permissions on the objects to be migrated |
| Destination PolarDB for MySQL cluster | The read and write permissions on the objects to be migrated |
Note For more information about how to create and authorize a database account, see
Create a database account.
Procedure
- At the top of the Migration Tasks page, select the region where the destination cluster resides.
- 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 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 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. - Select the migration types and the objects to be migrated.
Setting Description Select the migration types - To perform only full 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, we recommend that you do not write data to the source database during full data migration. This ensures data consistency between the source and destination databases.Select the objects to be migrated Select one or more objects from the Available section and click the
icon to move the objects to the Selected section. Notice- You can select columns, tables, or databases as the objects to be migrated.
- By default, after an object is migrated to the destination database, the name of the object remains unchanged. You can use the object name mapping feature to rename the objects that are migrated to the destination database. For more information, see Object name mapping.
- If you use the object name mapping feature to rename an object, other objects that are dependent on the object may fail to be migrated.
Specify whether to rename objects You can use the object name mapping feature to rename the objects that are migrated to the destination instance. For more information, see Object name mapping. Specify the retry time for failed connections to the source or destination database By default, if DTS fails to connect to the source or destination database, DTS retries within the next 720 minutes (12 hours). You can specify the retry time based on your needs. If DTS reconnects to the source and destination databases within the specified time, DTS resumes the data migration task. Otherwise, the data migration task fails. Note When DTS retries a connection, you are charged for the DTS instance. We recommend that you specify the retry time based on your business needs. You can also release the DTS instance at your earliest opportunity after the source and destination instances are released.Specify whether to copy temporary tables to the destination database when DMS performs online DDL operations on the source table If you use Data Management (DMS) to perform online DDL operations on the source database, you can specify whether to migrate temporary tables generated by online DDL operations. - Yes: DTS migrates the data of temporary tables generated by online DDL operations.
Note If online DDL operations generate a large amount of data, the data migration task may be delayed.
- No: DTS does not migrate the data of temporary tables generated by online DDL operations. Only the original DDL data of the source database is migrated.
Note If you select No, the tables in the destination database may be locked.
- In the lower-right corner of the page, click Precheck.
Note
- Before you can start the data migration task, a precheck is performed. You can start the data migration task only after the task passes the precheck.
- If the task fails to pass the precheck, you can click the
icon next to each failed item to view details.
- You can troubleshoot the issues based on the causes and run a precheck again.
- If you do not need to troubleshoot the issues, you can ignore failed items and run a precheck again.
- Click Buy and Start to start the data migration task.
- Schema migration and full data migration
We recommend that you do not manually stop the task during full data migration. Otherwise, the data migrated to the destination database will be incomplete. You can wait until the data migration task automatically stops.
- Schema migration, full data migration, and incremental data migration
The task does not automatically stop during incremental data migration. You must manually stop the task.
Notice We recommend that you select an appropriate time to manually stop the data migration task. For example, you can stop the task during off-peak hours or before you switch your workloads to the destination cluster.- 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.
- Wait until the status of incremental data migration changes to The migration task is not delayed again. Then, manually stop the migration task.
- Schema migration and full data migration
What to do next
The database accounts that are used for data migration have the read and write permissions. After data migration is complete, you must delete the database accounts to ensure security.