Migrate RDS MySQL to PolarDB-X 2.0 - Data Transmission Service

Supported source databases

The following types of MySQL source databases can be migrated to a PolarDB-X 2.0 instance. This topic uses an ApsaraDB RDS for MySQL instance as an example. The procedure is similar for other source databases.

An ApsaraDB RDS for MySQL instance.
The following types of self-managed databases:
- Self-managed database with a public IP address
- Self-managed database that is hosted on Elastic Compute Service (ECS)
- Self-managed database that is connected over Express Connect, VPN Gateway, or Smart Access Gateway
- Self-managed database that is connected over Database Gateway

Prerequisites

You have created a PolarDB-X 2.0 instance.
The PolarDB-X 2.0 instance must have more storage space than the ApsaraDB RDS for MySQL instance uses.

Limitations

Note

DTS migrates foreign keys during schema migration.
During full and incremental data migration, DTS temporarily disables constraint checks and foreign key cascades at the session level. Cascade updates or deletes on the source database while the task runs may cause data inconsistency.

Type	Description
Source database limits	Bandwidth requirement: The server hosting the source database must have sufficient outbound bandwidth. Otherwise, migration speed will drop. Each table to migrate must have a primary key or UNIQUE constraint, and the key columns must contain unique values. Otherwise, duplicate records may appear in the destination database. If you select tables as the migration objects and edit them—for example, by mapping column names—a single migration task supports up to 1,000 tables. If you exceed this limit, the task fails with an error when submitted. To fix this, split the tables across multiple tasks or configure a full-database migration task. If you need incremental migration, enable binary logging: Set binlog_format to ROW and binlog_row_image to FULL. Otherwise, the precheck fails and the task cannot start. Important If your self-managed MySQL source is a dual-master cluster—where each instance acts as both master and slave—enable the log_slave_updates parameter. This ensures DTS can read all binary logs. For RDS for MySQL instances, retain local binary logs for at least three days (seven days recommended). For self-managed MySQL databases, retain local binary logs for at least seven days. If DTS cannot access binary logs, the task fails. In extreme cases, data inconsistency or data loss may occur. Issues caused by binary log retention periods shorter than DTS requires are not covered under the DTS SLA. Note To set the retention period for local binary logs on an RDS for MySQL instance, see Automatically delete local logs. Operations not allowed on the source database: Do not run DDL operations that change database or table schemas during full migration. Otherwise, the migration task fails. Note During full migration, DTS queries the source database. This creates metadata locks that may block DDL operations on the source database. If you run only full migration, do not write new data to the source instance. Otherwise, source and destination data become inconsistent. To keep data consistent in real time, select full migration and incremental migration. DTS does not migrate data generated by changes that do not write to binary logs. Examples include data restored from physical backups or created by cascade operations. Note If this occurs, re-run full migration after your business allows it. If your source MySQL database is version 8.0.23 or later and contains invisible hidden columns, DTS cannot read those columns. This may cause data loss. Note Run `ALTER TABLE <table_name> ALTER COLUMN <column_name> SET VISIBLE;` to make the hidden column visible. For more information, see Invisible Columns. MySQL compatibility: When DTS migrates data from a MySQL-family source database, it relies on the standard MySQL protocol and Binlog format, and behaviors incompatible with standard MySQL are not supported. If your source database claims MySQL compatibility but behaves differently from MySQL (for example, when OceanBase is connected as a source in MySQL mode, the timestamp of the trailing rotate event in the Binlog is 0, which differs from MySQL), the DTS migration task may fail.
Other limits	If a primary key or unique key conflict occurs during migration: If the table schemas are consistent and a record in the destination database has the same primary key value as a record in the source database: During full migration, DTS keeps the record in the destination database. The record from the source database is not migrated. During incremental migration, DTS does not keep the record in the destination database. The record from the source database overwrites the record in the destination database. If the table schemas are inconsistent, only some columns of data may be migrated, or the migration may fail. Proceed with caution. If your source database uses temporary-table-mode online DDL operations—including multi-table merge scenarios—or adds function-based indexes to unique key columns, data loss or task failure may occur on the destination database. Before migration, assess the performance of both source and destination databases. Run migration during off-peak business hours. Otherwise, full migration consumes read and write resources on both databases and increases database load. Full migration runs INSERT operations concurrently. This fragments destination tables. After full migration, destination tables require more storage space than source tables. Confirm that DTS migration precision for FLOAT or DOUBLE columns meets your business needs. DTS reads these columns using `ROUND(COLUMN,PRECISION)`. If no precision is defined, DTS uses 38 digits for FLOAT and 308 digits for DOUBLE. DTS tries to recover failed tasks within seven days. Before switching traffic to the destination instance, end or release the task. Or run the `revoke` command to remove DTS’s write permission on the destination instance account. This prevents automatic recovery from overwriting destination data with source data. If your RDS for MySQL instance has Always-Encrypted enabled, full migration is not supported. Note RDS for MySQL instances with Transparent Data Encryption (TDE) enabled support schema migration, full migration, and incremental migration. If a task fails, DTS support staff will attempt to restore it within eight hours. During restoration, they may restart the task or adjust its parameters. Note Only DTS task parameters are modified—not database parameters. Parameters that may be adjusted include those listed in Modify instance parameters. If the destination PolarDB-X 2.0 table has auto partitioning enabled (`auto_partition=true`), each DDL statement executed on the source can contain only one `alter_specification`. Otherwise, DTS reports an error (`TDDL-4998`: `Multi alter specifications when create GSI not support yet`). To execute a DDL statement that contains multiple `alter_specification` items, split each `alter_specification` into a separate DDL statement and execute them one by one. For more information, see ALTER TABLE (DRDS mode) and ALTER TABLE (AUTO mode).
Special cases	For self-managed MySQL sources: A master–standby switchover on the source database causes the migration task to fail. DTS calculates latency by comparing the timestamp of the last record migrated to the destination database with the current time. If no DML operations run on the source for a long time, latency reporting becomes inaccurate. If latency appears too high, run a DML operation on the source to update the latency value. Note If you select full-database migration, create a heartbeat table. Update or write to it every second. DTS periodically runs CREATE DATABASE IF NOT EXISTS `test` on the source database to advance the binary log offset. If your source is Amazon Aurora MySQL or another clustered MySQL instance, ensure the domain name or IP address configured for the task—and its DNS resolution—always points to a read–write (RW) node. Otherwise, the migration task may fail. For RDS for MySQL sources: If you need incremental migration, RDS for MySQL instances that do not record transaction logs—such as RDS for MySQL 5.6 read-only instances—are not supported as sources. DTS periodically runs CREATE DATABASE IF NOT EXISTS `test` on the source database to advance the binary log offset.

Billing

Migration type	Instance configuration fee	Internet traffic fee
Schema migration and full data migration	Free of charge.	When the Access Method parameter of the destination database is set to Public IP Address, you are charged for Internet traffic. For more information, see Billing overview.
Incremental data migration	Charged. For more information, see Billing overview.

Migration types

Schema migration

Data Transmission Service (DTS) migrates the schema definitions of the migration objects from the source database to the destination database.
- DTS supports schema migration for tables, views, triggers, stored procedures, and functions.
  
  Note
  The routine_body of stored procedures, the routine_body of functions, and the select_statement of views are not modified.
- During schema migration, DTS changes the `DEFINER` to `INVOKER` for the views, stored procedures, and functions to be migrated. This action changes the value of `SQL SECURITY` to `INVOKER`. DTS also sets the `DEFINER` to the destination database account that is used for the migration task.
  
  Note
  The security authentication method and definer of the source database are not modified.
- Because DTS does not migrate user information, you must grant read and write permissions to the invoker to call views, stored procedures, and functions in the destination database.
Full migration

DTS migrates all historical data of the specified migration objects from the source database to the destination database.
Incremental migration

After a full migration is complete, DTS migrates incremental data updates from the source database to the destination database. Incremental migration lets you smoothly migrate data without interrupting your self-managed applications.

Supported SQL operations for incremental migration

Type	SQL statement
DML	INSERT, UPDATE, and DELETE
DDL	ALTER TABLE and ALTER VIEW CREATE FUNCTION, CREATE INDEX, CREATE PROCEDURE, CREATE TABLE, and CREATE VIEW DROP INDEX and DROP TABLE RENAME TABLE Important A RENAME TABLE operation may cause data inconsistency. For example, if you select only one table as the migration object and rename the table in the source instance during migration, the data of this table is not migrated to the destination database. To prevent this issue, select the entire database to which the table belongs as the migration object when you configure the data migration task. Make sure that the databases to which the table belongs before and after the RENAME TABLE operation are both included in the migration objects. TRUNCATE TABLE

Database account permissions

Database	Schema migration	Full data migration	Incremental data migration
ApsaraDB RDS for MySQL instance	SELECT permission	SELECT permission	REPLICATION CLIENT, REPLICATION SLAVE, SHOW VIEW, and SELECT permissions
PolarDB-X instance	read and write permissions

To create and authorize database accounts, see:

For an ApsaraDB RDS for MySQL instance, see Create an account and Modify the permissions of a standard account on an ApsaraDB RDS for MySQL instance.
For a PolarDB-X instance, see Manage database accounts.

Procedure

Navigate to the migration task list page for the destination region using one of the following methods.
From the DTS console
1. Log on to the Data Transmission Service (DTS) console.
2. In the navigation pane on the left, click Data Migration.
3. In the upper-left corner of the page, select the region where the migration instance is located.
From the DMS console

Note
The actual operations may vary based on the mode and layout of the DMS console. For more information, see Simple mode console and Customize the layout and style of the DMS console.
1. Log on to the Data Management (DMS) console.
2. In the top menu bar, choose Data + AI > Data Transmission (DTS) > Data Migration.
3. To the right of Data Migration Tasks, select the region where the migration instance is located.
Click Create Task to navigate to the task configuration page.

Configure the source and destination databases.

Warning

After you select the source and destination instances, we recommend that you carefully read the limits displayed at the top of the page. Otherwise, the task may fail or data inconsistency may occur.

Category	Parameter	Description
N/A	Task Name	DTS automatically generates a task name. We recommend that you specify a descriptive name for easy identification. The name does not need to be unique.
Source Database	Select Existing Connection	To use a database instance that has been added to the system (created or saved), select the desired database instance from the drop-down list. The database information below will be automatically configured. Note In the DMS console, this parameter is named Select a DMS database instance.. If you have not registered the database instance with the system, or do not need to use a registered instance, manually configure the database information below.
	Database Type	Select MySQL.
	Access Method	Select Alibaba Cloud Instance.
	Instance Region	Select the region of the source ApsaraDB RDS for MySQL instance.
	Cross-account	In this example, the migration occurs within the same Alibaba Cloud account. Select No.
	RDS Instance ID	Select the source ApsaraDB RDS for MySQL instance.
	Database Account	Enter the database account of the source ApsaraDB RDS for MySQL instance. For information about the permission requirements, see Permission requirements for database accounts.
	Database Password	Enter the password for the database account.
	Connection Method	Select Non-encrypted or SSL-encrypted based on your database requirements. If you set this parameter to SSL-encrypted, you must enable SSL encryption for the RDS for MySQL instance beforehand. For more information, see Quickly enable SSL encryption using a cloud certificate.
Destination Database	Select Existing Connection	To use a database instance that has been added to the system (created or saved), select the desired database instance from the drop-down list. The database information below will be automatically configured. Note In the DMS console, this parameter is named Select a DMS database instance.. If you have not registered the database instance with the system, or do not need to use a registered instance, manually configure the database information below.
	Database Type	Select PolarDB-X 2.0.
	Access Method	Select Alibaba Cloud Instance.
	Instance Region	Select the region where the destination PolarDB-X 2.0 instance resides.
	Instance ID	Select the destination PolarDB-X 2.0 instance.
	Database Account	Enter the database account of the destination PolarDB-X 2.0 instance. For information about the permission requirements, see Permission requirements for database accounts.
	Database Password	Enter the password for the database account.

After you complete the configuration, click Test Connectivity and Proceed at the bottom of the page.
Note
- Ensure that the IP address segment of the DTS service is automatically or manually added to the security settings of the source and destination databases to allow access from DTS servers. For more information, see Add DTS server IP addresses to a whitelist.
- If the source or destination database is a self-managed database (the Access Method is not Alibaba Cloud Instance), you must also click Test Connectivity in the CIDR Blocks of DTS Servers dialog box that appears.

Configure the task objects.

On the Configure Objects page, configure the objects that you want to migrate.

Parameter	Description
Migration Types	If you only need to perform a full migration, select both Schema Migration and Full Data Migration. To perform a migration with no downtime, select Schema Migration, Full Data Migration, and Incremental Data Migration. Note If you do not select Schema Migration, you must ensure that a database and tables to receive the data exist in the destination database. You can also use the object name mapping feature in the Selected Objects box as needed. If you do not select Incremental Data Migration, do not write new data to the source instance during data migration to ensure data consistency.
Processing Mode for Existing Destination Tables	Precheck and Report Errors: Checks whether tables with the same names exist in the destination database. If no tables with the same names exist, the precheck is passed. If tables with the same names exist, an error is reported during the precheck, and the data migration task does not start. Note If a table in the destination database has the same name but cannot be easily deleted or renamed, you can change the name of the table in the destination database. For more information, see Object name mapping. Ignore Errors and Proceed: Skips the check for tables with the same names. Warning Selecting Ignore Errors and Proceed may cause data inconsistency and business risks. For example: If the table schemas are consistent and a record in the destination database has the same primary key value as a record in the source database: During full migration, DTS keeps the record in the destination database. The record from the source database is not migrated. During incremental migration, DTS does not keep the record in the destination database. The record from the source database overwrites the record in the destination database. If the table schemas are inconsistent, only some columns of data may be migrated, or the migration may fail. Proceed with caution.
Source Objects	In the Source Objects box, click the objects to migrate, and then click to move them to the Selected Objects box. Note The granularity for selecting migration objects is schema, table, and column. If you select only tables or columns as migration objects, other objects such as views, triggers, and stored procedures are not migrated to the destination database.
Selected Objects	To change the name of a single migration object in the target instance, right-click the object in the Selected Objects box. For more information, see Map individual schema, table, and column names. To change the names of multiple migration objects in the target instance, click Selected Objects in the upper-right corner of the Batch Edit box. For more information, see Map multiple schema, table, and column names. Note If you use the object name mapping feature, the migration of other objects that depend on the mapped object may fail. To filter data by using WHERE conditions, right-click a table in the Selected Objects pane and specify the filter conditions in the dialog box that appears. For more information, see Set filter conditions. To select the DDL or DML operations for incremental data migration at the database or table level, right-click a migration object in the Selected Objects pane and select the required DML and DDL operations in the dialog box that appears.

Click Next: Advanced Settings to configure advanced parameters.

Parameter	Description
Dedicated Cluster for Task Scheduling	By default, DTS schedules tasks on a shared cluster. You do not need to select one. If you want more stable tasks, you can purchase a dedicated cluster to run DTS migration tasks.
Retry Time for Failed Connections	After the migration task starts, if the connection to the source or destination database fails, DTS reports an error and immediately begins to retry the connection. The default retry duration is 720 minutes. You can customize the retry time to a value from 10 to 1440 minutes. We recommend that you set the duration to more than 30 minutes. If DTS reconnects to the source and destination databases within the specified duration, the migration task automatically resumes. Otherwise, the task fails. Note For multiple DTS instances that share the same source or destination, the network retry time is determined by the setting of the last created task. Because you are charged for the task during the connection retry period, we recommend that you customize the retry time based on your business needs, or release the DTS instance as soon as possible after the source and destination database instances are released.
Retry Time for Other Issues	After the migration task starts, if a non-connectivity issue, such as a DDL or DML execution exception, occurs in the source or destination database, DTS reports an error and immediately begins to retry the operation. The default retry duration is 10 minutes. You can customize the retry time to a value from 1 to 1440 minutes. We recommend that you set the duration to more than 10 minutes. If the related operations succeed within the specified retry duration, the migration task automatically resumes. Otherwise, the task fails. Important The value of Retry Time for Other Issues must be less than the value of Retry Time for Failed Connections.
Enable Throttling for Full Data Migration	During full migration, DTS consumes read and write resources on the source and destination databases, which may increase the database load. If required, you can enable throttling for the full migration task. You can set Queries per second (QPS) to the source database, RPS of Full Data Migration, and Data migration speed for full migration (MB/s) to reduce the load on the destination database. Note This configuration item is available only if you select Full Data Migration for Migration Types. You can also adjust the full migration speed after the migration instance is running.
Enable Throttling for Incremental Data Migration	If required, you can also choose to set speed limits for the incremental migration task. You can set RPS of Incremental Data Migration and Data migration speed for incremental migration (MB/s) to reduce the load on the destination database. Note This configuration item is available only if you select Incremental Data Migration for Migration Types. You can also adjust the incremental migration speed after the migration instance is running.
Environment Tag	You can select an environment tag to identify the instance. In this example, you do not need to select a tag.
Whether to delete SQL operations on heartbeat tables of forward and reverse tasks	Choose whether DTS writes heartbeat SQL information to the source database while the instance is running. Yes: Does not write heartbeat SQL information to the source database. The DTS instance may display latency. No: Writes heartbeat SQL information to the source database. This may interfere with source database operations like physical backups and cloning.
Configure ETL	Based on your business needs, select whether to configure the ETL feature to process data. Yes: Configures the ETL feature. You must also enter data processing statements in the text box. No: Does not configure the ETL feature.
Monitoring and Alerting	Select whether to set alerts and receive alert notifications based on your business needs. No: Does not set an alert. Yes: Configure alerts by setting an alert threshold and an alert notifications. If a migration fails or the latency exceeds the threshold, the system sends an alert notification.

Click Next: Data Validation to configure a data validation task.

For more information about the data validation feature, see Configure data validation.

Save the task and run a precheck.
- To view the parameters for configuring this instance when you call the API operation, move the pointer over the Next: Save Task Settings and Precheck button and click Preview OpenAPI parameters in the bubble that appears.
- If you do not need to view or have finished viewing the API parameters, click Next: Save Task Settings and Precheck at the bottom of the page.
Note
- Before the migration task starts, DTS performs a precheck. The task starts only after it passes the precheck.
- If the precheck fails, click View Details next to the failed check item, fix the issue based on the prompt, and then run the precheck again.
- If a warning is reported during the precheck:
  
  For check items that cannot be ignored, click View Details next to the failed item, fix the issue based on the prompt, and then run the precheck again.
  
  For check items that can be ignored, you can click Confirm Alert Details, Ignore, OK, and Precheck Again to skip the alert item and run the precheck again. If you choose to ignore a warning, it may cause issues such as data inconsistency and pose risks to your business.

Purchase the migration instance.

When the Success Rate is 100%, click Next: Purchase Instance.

On the Purchase page, select the link specification for the data migration instance. For more information, see the following table.

Category	Parameter	Description
New Instance Class	Resource Group Settings	Select the resource group to which the instance belongs. The default value is default resource group. For more information, see What is Resource Management?
New Instance Class	Instance Class	DTS provides migration specifications with different performance levels. The link specification affects the migration speed. You can select a specification based on your business scenario. For more information, see Data migration link specifications.

After the configuration is complete, read and select Data Transmission Service (Pay-as-you-go) Service Terms.
Click Buy and Start. In the OK dialog box that appears, click OK.

You can view the progress of the migration task on the Data Migration Tasks list page.
Note
- If the migration task does not include incremental migration, it stops automatically after the full migration is complete. After the task stops, its Status changes to Completed.
- If the migration task includes incremental migration, it does not stop automatically. The incremental migration task continues to run. While the incremental migration task is running, the Status of the task is Running.