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 performance, high availability, high reliability, and ease of use. This topic describes how to migrate data between PolarDB for MySQL clusters that are owned by different Alibaba Cloud accounts by using Data Transmission Service (DTS).

Prerequisites

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
  • 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 The read permission 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.

Before you begin

  1. Log on to the Alibaba Cloud Management Console by using the Alibaba Cloud account that owns the source PolarDB for MySQL cluster.
  2. Create a RAM role and authorize this role to access the cloud resources of the Alibaba Cloud account that owns the source PolarDB for MySQL cluster. For more information, see Configure RAM authorization for data migration or synchronization from a user-created database in a VPC across different Alibaba Cloud accounts.
    Note To migrate data between PolarDB for MySQL clusters of different Alibaba Cloud accounts, you can specify the source PolarDB for MySQL cluster as a self-managed database connected over Express Connect. You can also request a public endpoint for the source PolarDB for MySQL cluster and specify the source cluster as a self-managed database with a public IP address. In this case, you do not need to create a RAM role and configure authorization.

Procedure

  1. Log on to the DTS console by using the Alibaba Cloud account that owns the destination PolarDB for MySQL cluster.
  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 cluster resides.
    Select a region
  4. In the upper-right corner of the page, click Create Migration Task.
  5. Select User-Created Database Connected over Express Connect, VPN Gateway, or Smart Access Gateway as the instance type. Then, click VPC of Another Alibaba Cloud Account next to the Peer VPC field.
    Note To migrate data between PolarDB for MySQL clusters of different Alibaba Cloud accounts, you can specify the source PolarDB for MySQL cluster as a self-managed database connected over Express Connect. You can also request a public endpoint for the source PolarDB for MySQL cluster and specify the source cluster as a self-managed database with a public IP address.
    Select a VPC across Alibaba Cloud accounts
  6. 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 specify an informative name for easy identification. You do not need to use a unique task name.
    Source Database Instance Type Select User-Created Database Connected over Express Connect, VPN Gateway, or Smart Access Gateway.
    Instance Region Select the region where the source PolarDB cluster resides.
    Alibaba Cloud Account ID Enter the ID of the Alibaba Cloud account that owns the source PolarDB cluster.
    Note To obtain the ID of the Alibaba Cloud account that owns the source PolarDB cluster, you must log on to the Account Management console by using this account. The account ID is displayed on the Security Settings page.
    Obtain the ID of the Alibaba Cloud account
    Role Name Enter the name of the RAM role that you created earlier in Before you begin.
    Peer VPC Select the ID of the VPC where the source PolarDB cluster resides.

    To obtain the VPC ID, you must log on to the PolarDB console by using the Alibaba Cloud account that owns the source PolarDB cluster. On the Clusters page, click the ID of the source PolarDB cluster. The VPC ID is displayed in the Basic Information section.

    View the VPC ID
    Database Type Select MySQL.
    IP Address Enter the private IP address of the source PolarDB cluster. In this example, enter 172.16.20.20.
    You can obtain the private IP address by pinging the VPC-facing endpoint of the source PolarDB cluster. Obtain the private IP address of the PolarDB cluster
    Port Number Enter the service port number of the source PolarDB cluster. The default port number is 3306.
    Database Account Enter the database account of the source PolarDB cluster. For information about the permissions that are required for the account, see Permissions required for database accounts.
    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. For information about the permissions that are required for the account, see Permissions required for database accounts.
    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 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.
  7. In the lower-right corner of the page, click Set Whitelist and Next.
    Note DTS adds the CIDR blocks of DTS servers to the whitelists of the source and destination PolarDB clusters. This ensures that DTS servers can connect to the source and destination PolarDB clusters.
  8. Select the migration types and the objects to be migrated.
    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 Rightwards arrow 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.
  9. 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 Info icon 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.
  10. After the task passes the precheck, click Next.
  11. In the Confirm Settings dialog box, specify the Channel Specification parameter and select Data Transmission Service (Pay-As-You-Go) Service Terms.
  12. 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.
      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 delay time 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. Stop a task during incremental 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.