Migrate PolarDB-X 2.0 to DataHub with DTS-Data Transmission Service(DTS)-阿里云帮助中心

Prerequisites

You have created a source PolarDB-X 2.0 instance. For more information, see Create an instance.
You have activated DataHub and created a project to store the migrated data. For more information, see Quick start (synchronization example) and Manage projects.

Limitations

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. Enterprise Edition PolarDB-X 2.0 read-only instances are not supported as a source database. 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 limitations on the source database: During schema migration and full data migration, do not perform DDL operations that change the database or table schema. Otherwise, the data migration task will fail. Note During full data migration, DTS queries the source database. This action places a metadata lock, which may block DDL operations on 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 in the source database while the task is running, data inconsistencies may result. If you need to change the network type of the PolarDB-X 2.0 instance during migration, you must update the network connection information of the migration task after the change 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. Migration of table groups (TABLEGROUP) and databases or tables with the Locality attribute is not supported. Migration of tables whose names are reserved words, such as `select`, is not supported. In a PolarDB-X 2.0 instance, database partitions in DRDS mode are not supported for synchronization. During the operation of a DTS migration task, changing the type of a broadcast table in the source PolarDB-X 2.0 instance (for example, changing a broadcast table to a regular table or a sharded table) is not supported. To change the table type, stop the migration task first, and then reconfigure the migration task after the change is complete.
Other limitations	Only table-level migration is supported. The maximum length of a string field in a destination DataHub topic is 2 MB. Before migrating data, evaluate the performance of your source and destination databases. Perform the migration during off-peak hours. A full migration consumes read and write resources on both databases, which can increase their load. DTS attempts to restore migration tasks that have failed within seven days. Therefore, before you switch your services 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 that is used to access the target instance. This prevents the source data from overwriting the data in the target instance after the task is automatically restored. 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.
Other precautions	DTS periodically updates the `dts_health_check`.`ha_health_check` table in the source database to advance the binlog position.

Billing

Migration type	Link configuration fee	Internet traffic fee
Schema migration	Free of charge.	This example is free of charge.
Incremental data migration	This is a paid feature. For more information, see Billing overview.	This example is free of charge.

Migration types

Schema migration

DTS migrates the schema definitions of the 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

Operation type	SQL statement
DML	INSERT, UPDATE, DELETE
DDL	ADD COLUMN Important If you manually modify the table structure in the target database, restart the task: pause and then start the task.

Database account permissions

Database	Schema migration	Incremental migration
PolarDB-X 2.0 instance	SELECT permission	The REPLICATION SLAVE and REPLICATION CLIENT permissions, and the SELECT permission on the objects to be migrated. Note For information about how to grant permissions, see Account permissions for data synchronization.

Data type mapping

For more information, see Data type mappings for schema migration.

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, read the Limits section displayed at the top of the page to ensure that you can create and run the migration task successfully.

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 2.0.
	Access Method	Select Alibaba Cloud Instance.
	Instance Region	Select the region where the source PolarDB-X 2.0 instance is located.
	Replicate Data Across Alibaba Cloud Accounts	In this example, data is migrated within the same Alibaba Cloud account. Select No.
	Instance ID	Select the ID of the source PolarDB-X 2.0 instance.
	Database Account	Enter the database account for the source PolarDB-X 2.0 instance. For permission requirements, see Database account permissions.
	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 DataHub.
	Access Method	Select Alibaba Cloud Instance.
	Instance Region	Select the region where the destination DataHub project is located.
	Project	Select the ID of the destination DataHub project.

After you complete the configuration, click Test Connectivity and Proceed at the bottom of the page.

Note
Ensure that the DTS service IP address segments are 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.

Configure the task objects.

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

Parameter	Description
Migration Types	For migrating data from PolarDB-X 2.0 to DataHub, only Schema Migration and Incremental Data Migration are supported. Select the migration types based on your business needs. Note If you select Schema Migration, foreign keys in the source database are also migrated to the destination database. If you do not select Incremental Data Migration, do not write new data to the source instance during data migration to ensure data consistency.
Naming Rules of Additional Columns	When DTS migrates data to DataHub, it adds additional columns to the destination table. If these new column names conflict with existing ones, the data migration fails. You must select either New Rule or Previous Rule based on your business needs. Warning Before you select a rule for additional columns, you must check whether the names of the additional columns will conflict with any existing columns in the destination table. For more information about the rules and definitions of additional columns, see Names and definitions of additional columns.
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	Select one or more objects from the Source Objects section. Click the icon and add the objects to the Selected Objects section. Note Migration objects can be selected at the database, table, or column level. If you select only tables as migration objects, other object types 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 renamed object might fail. To filter data by using WHERE clauses, right-click a table to be migrated in the Selected Objects box and set the filter conditions in the dialog box that appears. For instructions, see Set filter conditions. To select SQL operations to migrate at the database or table level, right-click the migration object in the Selected Objects box and select the desired SQL 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 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.
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.
Environment Tag	You can select an environment tag to identify the instance. No selection is needed for this example.
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 contact. 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.