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 from a self-managed MySQL database to a PolarDB for MySQL cluster 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.
  • DTS uses the ROUND(COLUMN,PRECISION) function to retrieve values from columns of the FLOAT or DOUBLE data type. If you do not specify a precision, DTS sets the precision for the FLOAT data type to 38 digits and the precision for the DOUBLE data type to 308 digits. You must check whether the precision settings meet your business requirements.
  • If a data migration task fails, DTS automatically resumes the task. Before you switch your workloads to the destination cluster, stop or release the data migration task. Otherwise, the data in the source database will overwrite the data in the destination cluster after the task is resumed.

Introduction to migration types

DTS supports schema migration, full data migration, and incremental data migration. For more information, see Terms.
Note When you select all of the three migration types, data between databases can be smoothly migrated.

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 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 Schema migration and full data migration Incremental data migration
Self-managed MySQL database The SELECT permission The REPLICATION CLIENT, REPLICATION SLAVE, SHOW VIEW, and SELECT permissions
PolarDB for MySQL cluster The read and write permissions The read and write permissions

For more information about how to create and authorize a database account, see the following topics:

Before you begin

Create an account for a user-created MySQL database and configure binary logging

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 cluster resides.
    Select a region
  4. In the upper-right corner of the page, click Create Migration Task.
  5. 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 an instance type based on the deployment of the source database. In this example, select User-Created Database with Public IP Address.
    Note If you select other instance types, you must deploy the network environment for the source database. For more information, see Preparation overview.
    Instance Region If the instance type is set to User-Created Database with Public IP Address, you do not need to specify the instance region.
    Note If a whitelist is configured for the self-managed MySQL database, you must add the CIDR blocks of DTS servers to the whitelist of the database. You can click Get IP Address Segment of DTS next to Instance Region to obtain the CIDR blocks of DTS servers.
    Database Type Select MySQL.
    Hostname or IP Address Enter the endpoint that is used to connect to the self-managed MySQL database. In this example, enter the public IP address.
    Port Number Enter the service port number of the self-managed MySQL database. The default port number is 3306.
    Database Account Enter the account of the self-managed MySQL database. For more 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 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 more 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 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.
  6. In the lower-right corner of the page, click Set Whitelist and Next.
    Note DTS adds the CIDR blocks of DTS servers to the whitelist of the destination PolarDB for MySQL cluster. This ensures that DTS servers can connect to the destination cluster.
  7. Select the migration types and the objects to be migrated.
    Select the objects to be migrated and the migration types
    Configuration Description
    Migration Types
    • To perform only full migration, select both 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, do not write new data to the source database during full data migration. This ensures that the data between the source and destination databases is consistent.
    Objects

    In the Available section, select the objects to be migrated. Then, click the Rightwards arrow icon to add them to the Selected section.

    Notice
    • You can select databases, tables, and columns as the objects to be migrated.
    • By default, the name of the migrated object in the destination database remains consistent with the name of the object in the source database. You can change the names of the objects that are migrated to the destination database by using the object name mapping feature. For more information, see Object name mapping.
    • If you use the object name mapping feature on an object, other objects that are dependent on the object may fail to be migrated.
  8. In the lower-right corner of the page, click Precheck.
    Notice
    • Before you can start the data migration task, a precheck is performed. DTS can migrate data only if the precheck is past.
    • If the precheck fails, click the Prompt icon next to each failed item to view details. Fix the issues as prompted and run the precheck again.
  9. After the precheck is past, click Next.
  10. In the Confirm Settings dialog box, specify the Channel Specification parameter and select 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 the migration task. Otherwise, the data may be incomplete. You need only to wait until the migration task is complete. The migration task can automatically stop.

    • Schema migration, full data migration, and incremental data migration

      The migration task cannot automatically stop. You must manually stop the migration task.

      Notice Manually stop the migration task at an appropriate time. For example, you can stop the migration task during off-peak hours of your business or before you switch your business 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 may appear in the status for incremental migration.
      2. Wait until the status of Incremental Data Migration for the migration task changes to The migration task is not delayed again. Then, manually stop the migration task.Stop an incremental migration task
  12. Switch your business to the PolarDB cluster.