Migrate data between PolarDB for MySQL clusters - Data Transmission Service

PolarDB is a next-generation distributed relational database service that is developed by Alibaba Cloud. PolarDB is compatible with the MySQL database engine and provides features such as high performance, 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 V8.0. However, you can create a PolarDB for MySQL cluster of V8.0, 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 Purchase an Enterprise Edition cluster.
The binary logging feature is enabled for the source PolarDB for MySQL cluster. For more information, see Enable binary logging.

Usage notes

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 Billing overview.
Incremental data migration	Charged. For more information, see Billing overview.

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 permissions
Source PolarDB for MySQL cluster	Read permissions on the objects to be migrated
Destination PolarDB for MySQL cluster	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 and manage a database account.

Procedure

Log on to the DTS console.
Note
If you are redirected to the Data Management (DMS) console, you can click the icon in the to go to the previous version of the DTS console.
In the left-side navigation pane, click Data Migration.
At the top of the Migration Tasks page, select the region where the destination cluster resides.
In the upper-right corner of the page, click Create Migration Task.

Configure the source and destination databases.

Configure the source and destination databases

Section	Parameter	Description
N/A	Task Name	The task name that DTS automatically generates. We recommend that you specify a descriptive name that makes it easy to identify the task. You do not need to specify a unique task name.
Source Database	Instance Type	Select PolarDB.
	Instance Region	Select the region in which 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 set the source database parameters, click Test Connectivity next to Database Password to check whether the information is valid. If the information is valid, the Passed message is displayed. If the Failed message is displayed, click Check next to Failed to modify the information based on the check results.
Destination Database	Instance Type	Select PolarDB.
	Instance Region	Select the region in which 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 set the destination database parameters, click Test Connectivity next to Database Password to check whether the information is valid. If the information is valid, the Passed message is displayed. If the Failed message is displayed, click Check next to Failed to modify the information based on the check results.

In the lower-right corner of the page, click Set Whitelist and Next.
Warning
If the CIDR blocks of DTS servers are automatically or manually added to the whitelist of the database or instance, or to the ECS security group rules, security risks may arise. Therefore, before you use DTS to migrate data, you must understand and acknowledge the potential risks and take preventive measures, including but not limited to the following measures: enhance the security of your username and password, limit the ports that are exposed, authenticate API calls, regularly check the whitelist or ECS security group rules and forbid unauthorized CIDR blocks, or connect the database to DTS by using Express Connect, VPN Gateway, or Smart Access Gateway.

Select the required migration types and the objects that you want to migrate.

Select the required migration types and the objects that you want to migrate

Setting	Description
Select 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. Important 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 that you want to migrate	Select one or more objects from the Available section and click the icon to add the objects to the Selected section. Important 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 database. For more information, see Object name mapping.
Specify the retry time range 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 range based on your business requirements. If DTS reconnects to the source and destination databases within the specified time range, DTS resumes the data migration task. Otherwise, the data migration task fails. Note Within the time range in which DTS attempts to reconnect to the source and destination databases, you are charged for the DTS instance. We recommend that you specify the retry time range based on your business requirements. You can also release the DTS instance at the earliest opportunity after the source and destination databases 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 DMS to perform online DDL operations on the source database, you can specify whether to migrate temporary tables generated by online DDL operations. Valid values: 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 take an extended period of time to complete. 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, DTS performs a precheck. 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.
After the task passes the precheck, click Next.
In the Confirm Settings dialog box, specify the Channel Specification parameter and select Data Transmission Service (Pay-As-You-Go) Service Terms.
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 may be incomplete. You can 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 task.
  Important
  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.
  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 latency of incremental data migration may be displayed in the progress bar.
  2. Wait until the status of incremental data migration changes to The migration task is not delayed again. Then, manually stop the migration task.
Switch your workloads to the destination PolarDB cluster.

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.