Migrate data from PolarDB-X 1.0 to ApsaraDB RDS for MySQL - Data Transmission Service

Prerequisites

A source PolarDB-X 1.0 instance is created. For more information, see Create a PolarDB-X 1.0 instance.

Note
The PolarDB-X 1.0 instance must use ApsaraDB RDS for MySQL as its storage type. This includes both privately customized and separately purchased RDS instances. PolarDB for MySQL is not supported.
To perform an incremental data migration, ensure that the character set of the data to be migrated is not utf8mb3. Otherwise, the incremental data migration task will fail.
A destination ApsaraDB RDS for MySQL instance is created with available storage space larger than the used storage space of the source PolarDB-X 1.0 instance. For more information, see Create an ApsaraDB RDS for MySQL instance.

Usage notes

Note

During schema migration, DTS migrates foreign keys from the source database to the destination database.

Type	Description
Source database limitations	Bandwidth requirements: The server that hosts the source database must have sufficient outbound bandwidth. Insufficient bandwidth will slow down the data migration. Tables to be migrated must have a PRIMARY KEY or a UNIQUE constraint, and the fields in the key or constraint must be unique. Otherwise, this may cause duplicate data in the destination database. If you migrate objects at the table level and need to edit them, for example, by mapping column names, a single data migration task supports a maximum of 1,000 tables. If you exceed this limit, the task submission will fail. In this case, split the tables into multiple data migration tasks or configure a task to migrate the entire database. For incremental data migration, the source database must meet the following binary log requirements: Enable the binary log feature, and set the `binlog_row_image` parameter to `full`. Otherwise, the precheck fails and the data migration task cannot start. For incremental data migration tasks, DTS requires that the binary logs of the source database be retained for at least 24 hours. For tasks that include both full data migration and incremental data migration, the binary logs must be retained for at least 7 days. You can change the retention period to 24 hours after the full data migration is complete. If the binary logs are not retained for the required period, DTS may fail to obtain them, which can cause task failures or even data inconsistency and loss. The DTS SLA does not cover issues caused by an insufficient binary log retention period. Operational restrictions on the source database: During data migration, do not perform operations such as scaling out, scaling in, migrating hot-spot tables, changing the sharding key, or executing DDL statements. Otherwise, the data migration task will fail. Note During the full migration phase, DTS queries the source database. This creates a metadata lock, which may block DDL operations on the source database. If the partition key is changed in the source database and the primary key in the target table does not include the source partition key, data loss may occur in the target database. Reason: A PolarDB-X 1.0 instance has multiple RDS for MySQL instances attached to it. DTS creates a separate migration link for each RDS for MySQL instance. A change to a partition key causes data to be deleted from one RDS for MySQL instance and inserted into another. Because the links execute independently, the execution order of the DELETE and INSERT operations is not guaranteed. If the primary key of the target database does not include the partition key, a DELETE operation that executes later may accidentally delete the newly inserted data. Recommendation: To prevent data loss caused by out-of-order operations, ensure that the primary key of the target table includes the partition key column from the source database. During full and incremental migration, DTS temporarily disables constraint checks and foreign key cascading operations at the session level. If cascading update or delete operations occur on the source database while the task is running, data inconsistency may occur. If you switch the network type of the PolarDB-X 1.0 instance during migration, update the migration link's network connection information after the switch is complete. If you perform only full data migration, do not write new data to the source database during the migration. Otherwise, data will become inconsistent between the source and destination databases. To maintain real-time data consistency, select schema migration, full data migration, and incremental data migration. The source PolarDB-X 1.0 instance must be version 5.2 or later. Do not change the type of a broadcast table in the source PolarDB-X 1.0 instance while a DTS migration task is running (for example, from a broadcast table to a single table or a sharded table). If you need to change the table type, stop the migration task. After the change is complete, reconfigure the migration task.
Other limitations	DTS relies on the continuity of XA transactions in the source PolarDB-X 1.0 instance to ensure data consistency for incremental migration tasks. If the continuity of XA transactions is broken, for example, during a disaster recovery scenario for the incremental data capture module, uncommitted XA transactions may be lost. Migration of INDEX and PARTITION is not supported. Migration of online DDL operations is not supported. If your data includes four-byte characters—such as rare Chinese characters or emojis—the destination database and table must use the utf8mb4 charset. Note If you use DTS to migrate schemas, set the instance-level parameter `character_set_server` to utf8mb4 in the destination database. Before you perform data migration, evaluate the performance of the source and target databases. We also recommend performing data migration during off-peak hours. Otherwise, DTS consumes read and write resources on both the source and target databases during full migration, which may increase the database load. Full migration runs concurrent INSERT operations, which can cause table fragmentation in the target database. As a result, tables in the target database will occupy more storage space than those in the source instance. DTS attempts to recover failed migration tasks within seven days. Therefore, before the cutover to the target instance, you must end or release the task, or use the `revoke` command to revoke the write permissions of the DTS account on the target instance. This prevents the source data from overwriting the data on the target instance if the task is automatically recovered. If you write columns with identical names but different cases into the same table in the destination MySQL database, unexpected results may occur. MySQL column names are case-insensitive. After migration completes—the task status is Status and the status changes to Completed—run `analyze table <table_name>` to confirm all data is written to the destination table. For example, after a high-availability (HA) switchover in the destination MySQL database, data may remain in memory and never reach disk, causing data loss. 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.
Additional considerations	DTS periodically updates the dts_health_check.ha_health_check table in the source database to advance the binlog position.

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

DTS migrates the schema definitions of the migration objects from the source database to 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.

SQL operations for incremental migration

Operation type	SQL statement
DML	INSERT, UPDATE, DELETE

Database account permissions

Database	Schema migration	Full data migration	Incremental data migration
PolarDB-X 1.0 instance	SELECT permission	SELECT permission	REPLICATION SLAVE, REPLICATION CLIENT, and SELECT permissions on the objects to be migrated. Note For information about how to grant permissions, see Account permission issues during data synchronization.
ApsaraDB RDS for MySQL instance	Read and write permissions

To create accounts and grant permissions:

For a PolarDB-X 1.0 instance, see Manage database accounts.
For an ApsaraDB RDS for MySQL instance, see Create an account and Modify account permissions.

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.

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 PolarDB-X 1.0.
	Connection Type	Select Alibaba Cloud Instance.
	Instance Region	Select the region where the source PolarDB-X 1.0 instance resides.
	Replicate Data Across Alibaba Cloud Accounts	In this example, a database instance under the current Alibaba Cloud account is used. Select No.
	Instance ID	Select the ID of the source PolarDB-X 1.0 instance.
	Database Account	Enter the database account for the source PolarDB-X 1.0 instance. For permission requirements, see Permissions required for database accounts.
	Database Password	Enter the password for the database account.
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 MySQL.
	Connection Type	Select Alibaba Cloud Instance.
	Instance Region	Select the region where the destination ApsaraDB RDS for MySQL instance resides.
	Replicate Data Across Alibaba Cloud Accounts	In this example, a database instance under the current Alibaba Cloud account is used. Select No.
	RDS Instance ID	Select the ID of the destination ApsaraDB RDS for MySQL instance.
	Database Account	Enter the database account for the destination ApsaraDB RDS for MySQL instance. For permission requirements, see Permissions required for database accounts.
	Database Password	Enter the password for the database account.
	Encryption	Choose either Non-encrypted or SSL-encrypted connection based on your requirements. If you choose SSL-encrypted, you must enable SSL encryption on the ApsaraDB RDS for MySQL instance beforehand. For more information, see Enable SSL encryption with a cloud certificate.

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 of Conflicting 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.
Capitalization of Object Names in Destination Instance	You can configure the case sensitivity policy for the names of migrated objects, such as databases, tables, and columns, in the destination instance. By default, DTS default policy is selected. You can also choose to keep the case sensitivity consistent with the default policy of the source or destination database. For more information, see Case sensitivity of object names in the destination database.
Source Objects	In the Source Objects box, click the objects to migrate, and then click to move them to the Selected Objects box. Note Select objects to migrate at the table level. If you select an entire database, any changes to add or delete tables in that database will not be migrated to the destination.
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 Using the object name mapping feature can cause the migration of dependent objects to fail. To filter data by using a WHERE clause, right-click the table to be migrated in the Selected Objects list and specify the filter condition in the dialog box. For instructions, see Set filter conditions. To select SQL operations to migrate at the database or table level, right-click the object in the Selected Objects list and select the desired SQL operations in the dialog box.

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 based on your needs. In this example, no tag is needed.
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.

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 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.