Apsara PolarDB is a next-generation relational database service that is developed by Alibaba Cloud. The service 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 user-created MySQL database to an Apsara 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 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%.
  • 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.

Migration types

DTS supports schema migration, full data migration, and incremental data migration. For more information, see Terms.
Note You can use these three migration types together to migrate data without service interruptions.

Billing

Migration type Instance configurations Internet traffic
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 Schema migration and full data migration Incremental data migration
User-created MySQL database The SELECT permission The REPLICATION CLIENT, REPLICATION SLAVE, SHOW VIEW, and SELECT permissions
Apsara PolarDB for MySQL cluster The read/write permissions The read/write permissions

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

Preparations

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 Migration Tasks the 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 for the data migration task.
    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 where the source database is deployed. In this example, select User-Created Database with Public IP Address.
    Note If you select other instance types, you must prepare the environments that are required 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 user-created 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 user-created MySQL database. In this example, enter the public IP address.
    Port Number Enter the service port number of the user-created MySQL database. The default port number is 3306.
    Database Account Enter the account of the user-created 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 source 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 more information about the permissions that are required for the account, see Permissions required for database accounts.
    Database Password Enter the password of the destination 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 Apsara PolarDB for MySQL cluster. This ensures that DTS servers can connect to the destination cluster.
  7. Configure migration types and objects.
    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 business disruptions, 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.
    • By default, the selected objects are not renamed after the migration. If you want to rename the objects that are migrated to the destination instance, you can use the object name mapping feature provided by DTS. For more information about how to use this feature, 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 Note icon 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.Stop the incremental migration task
  12. Switch your workloads to the destination cluster.