Migrate data from PolarDB-X 2.0 to PolarDB-X 1.0 - Data Transmission Service

This topic describes how to use Data Transmission Service (DTS) to migrate data from a PolarDB-X 2.0 instance to a PolarDB-X 1.0 instance.

Important

This feature is in canary release and is available only to some users.

Prerequisites

Create a destination PolarDB-X 1.0 instance. The storage space of the destination instance must be larger than the amount of data that you want to migrate from the source PolarDB-X 2.0 instance. For more information, see Create a PolarDB-X 1.0 instance.
Create a database and tables in the destination PolarDB-X 1.0 instance for the migrated data. For more information, see Create a database and Execute basic SQL operations.
Note
Use the same names for the destination database and tables in the PolarDB-X 2.0 instance as those in the source database. Otherwise, use the schema mapping feature in the Selected Objects section on the Configure Objects page when you configure the task.

Precautions

Type	Description
Source database limits	Bandwidth requirements: The server to which the source database belongs must have sufficient outbound bandwidth. Otherwise, the data migration speed is affected. The source database does not support read-only instances of Enterprise Edition PolarDB-X 2.0. Migration objects: Tables whose names contain uppercase letters cannot be migrated. The data migration instance does not support the TABLEGROUP and the database or schema that contains Locality attribute. Tables whose names are reserved words, such as `select`, cannot be migrated. The tables to be migrated must have PRIMARY KEY or UNIQUE constraints, and all fields must be unique. Otherwise, the destination database may contain duplicate data records. If you select tables as the objects to be migrated and you need to modify the tables in the destination database, such as renaming tables or columns, you can migrate up to 1,000 tables in a single data migration task. If you run a task to migrate more than 1,000 tables, a request error occurs. In this case, we recommend that you split the tables to be migrated, configure multiple tasks to migrate the tables, or configure a task to migrate the entire database. Binary logging is enabled by default in PolarDB-X 2.0 instances. If you want to migrate incremental data, you must ensure that the binlog_row_image parameter is set to full. Otherwise, error messages are returned during the precheck and the data migration task fails to be started. For more information, see Parameter settings. During full data migration, do not perform DDL operations that change the schema of the database or tables. Otherwise, the data migration task fails. Note During full data migration, DTS queries the source database. This creates metadata locks that may block DDL operations on the source database. If you perform only full data migration, do not write new data to the source database. Otherwise, data inconsistency between the source and destination databases occurs. To ensure real-time data consistency, select both full data migration and incremental data migration. If the network information of the PolarDB-X 2.0 instance changes, the migration instance may experience a delay for a period of time.
Other limits	DTS periodically attempts to execute the CREATE DATABASE IF NOT EXISTS `test` command on the source database to create the `test` database and write heartbeat data to advance the Binlog offset. If you set the Whether to delete SQL operations on heartbeat tables of forward and reverse tasks option to Yes when you configure a migration instance (or if the source database account used by the migration instance does not have the permission to create databases), and no DML operations are performed on the source database for an extended period, the latency information may become inaccurate. Note If the migration instance shows a long latency, you can perform a DML operation on the source database to update the latency information. During full data migration, DTS consumes some read and write resources of the source and destination databases. This may increase the database load. Before you migrate data, evaluate the performance of the source and destination databases. Perform data migration during off-peak hours. For example, you can perform data migration when the CPU loads of the source and destination databases are below 30%. Full data migration involves concurrent INSERT operations. This causes table fragmentation in the destination database. After full data migration is complete, the storage space occupied by the tables in the destination database is larger than that in the source database. During the migration, if data is written to the destination database from sources other than DTS, data inconsistency between the source and destination databases may occur. This may even cause the migration instance to fail. If an instance fails, DTS helpdesk will try to recover the instance within 8 hours. During the recovery process, operations such as restarting the instance and adjusting parameters may be performed. Note When parameters are adjusted, only the parameters of the DTS instance are modified. The parameters of the database are not modified. The parameters that may be modified include but are not limited to those described in Modify instance parameters.

Billing

Migration type	Task configuration fee	Data transfer fee
Full Data Migration	Free of charge.	Free of charge in this example. 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 Billable items.
Incremental Data Migration	Charged. For more information, see Billing overview.

SQL operations supported for incremental migration

Operation type	SQL statement
DML	INSERT, UPDATE, DELETE
DDL	CREATE TABLE, RENAME TABLE, ALTER TABLE, DROP TABLE, TRUNCATE TABLE, CREATE INDEX, DROP INDEX Note Only CREATE TABLE operations for single tables can be migrated. CREATE TABLE operations for sharded databases and tables cannot be migrated. If the source database is an Enterprise Edition PolarDB-X 2.0 instance, CREATE INDEX operations cannot be migrated. RENAME TABLE operations may cause data inconsistency between the source and destination databases. For example, if you select a table as the object to be migrated and rename the table during data migration, the data of this table is not migrated to the destination database. To prevent this situation, you can select the database to which this table belongs as the object to be migrated 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 added to the objects to be migrated.

Permissions required for database accounts

Database	Full migration	Incremental migration
Source PolarDB-X 2.0	SELECT permission.	REPLICATION SLAVE, REPLICATION CLIENT, and SELECT on the objects to be migrated.
Destination PolarDB-X 1.0 instance	Read and write.

To create a database account and grant permissions:

For a PolarDB-X 2.0 instance, see Manage database accounts and Account permission issues during data synchronization.
For a PolarDB-X 1.0 instance, see Manage database accounts.

Procedure

Use one of the following methods to go to the Data Migration page and select the region in which the data migration instance resides.
DTS console
1. Log on to the DTS console.
2. In the left-side navigation pane, click Data Migration.
3. In the upper-left corner of the page, select the region in which the data migration instance resides.
DMS console
Note
The actual operation may vary based on the mode and layout of the DMS console. For more information, see Simple mode and Customize the layout and style of the DMS console.
1. Log on to the DMS console.
2. In the top navigation bar, move the pointer over Data + AI > DTS (DTS) > Data Migration.
3. From the drop-down list to the right of Data Migration Tasks, select the region in which the data synchronization instance resides.
Click Create Task to go to the task configuration page.

Configure the source and destination databases. The following table describes the parameters.

Category	Configuration	Description
None	Task Name	The name of the DTS task. DTS automatically generates a task name. We recommend that you specify an informative name that makes it easy to identify the task. You do not need to specify a unique task name.
Source Database	Select Existing Connection	If you use a database instance that is registered with DTS, select the instance from the drop-down list. DTS automatically populates the following database parameters for the instance. For more information, see Manage database connections. Note In the DMS console, you can select the database instance from the Select a DMS database instance drop-down list. If you fail to register the instance with DTS, or you do not need to use the instance that is registered with DTS, you must configure the following database information.
	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 resides.
	Replicate Data Across Alibaba Cloud Accounts	In this example, a database instance of the current Alibaba Cloud account is used. Select No.
	Instance ID	Select the ID of the source PolarDB-X 2.0 instance.
	Database Account	Enter the database account of the source PolarDB-X 2.0 instance. For more information about the required permissions, see Permissions required for database accounts.
	Database Password	The password that is used to access the database instance.
Destination Database	Select Existing Connection	If you use a database instance that is registered with DTS, select the instance from the drop-down list. DTS automatically populates the following database parameters for the instance. For more information, see Manage database connections. Note In the DMS console, you can select the database instance from the Select a DMS database instance drop-down list. If you fail to register the instance with DTS, or you do not need to use the instance that is registered with DTS, you must configure the following database information.
	Database Type	Select PolarDB-X 1.0.
	Access Method	Select Alibaba Cloud Instance.
	Instance Region	Select the region where the destination PolarDB-X 1.0 instance resides.
	Instance ID	Select the ID of the destination PolarDB-X 1.0 instance.
	Database Account	Enter the database account of the destination PolarDB-X 1.0 instance. For more information about the required permissions, see Permissions required for database accounts.
	Database Password	The password that is used to access the database instance.

In the lower part of the page, click Test Connectivity and Proceed.
Note
Make sure that the CIDR blocks of DTS servers can be 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 objects to be migrated.

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

Configuration	Description
Migration Types	To perform only full data migration, select only Full Data Migration. To ensure service continuity during data migration, select Full Data Migration and Incremental Data Migration. Note If you do not select Incremental Data Migration, we recommend that you do not write data to the source database during data migration. This ensures data consistency between the source and destination databases.
Incremental CDC Type	Select a type based on the log engine of the PolarDB-X 2.0 instance. Note This parameter is available only if you set Migration Types to Incremental Data Migration. Before you select Multi-stream Change Data Capture (CDC), ensure that multi-stream is enabled for the PolarDB-X 2.0 instance. For more information, see Enable multi-stream.
Processing Mode of Conflicting Tables	Precheck and Report Errors: checks whether the destination database contains tables that use the same names as tables in the source database. If the source and destination databases do not contain tables that have identical table names, the precheck is passed. Otherwise, an error is returned during the precheck and the data migration task cannot be started. Note If the source and destination databases contain tables with identical names and the tables in the destination database cannot be deleted or renamed, you can use the object name mapping feature to rename the tables that are migrated to the destination database. For more information, see Map object names. Ignore Errors and Proceed: skips the precheck for identical table names in the source and destination databases. Warning If you select Ignore Errors and Proceed, data inconsistency may occur and your business may be exposed to the following potential risks: If the source and destination databases have the same schema, and a data record has the same primary key as an existing data record in the destination database, the following scenarios may occur: During full data migration, DTS does not migrate the data record to the destination database. The existing data record in the destination database is retained. During incremental data migration, DTS migrates the data record to the destination database. The existing data record in the destination database is overwritten. If the source and destination databases have different schemas, only specific columns are migrated or the data migration task fails. Proceed with caution.
Source Objects	Select one or more objects from the Source Objects section. Click the icon to add the objects to the Selected Objects section. Note You can select databases or tables as migration objects.
Selected Objects	To specify the name of an object to be migrated in the destination instance or specify the object to receive data in the destination instance, right-click the object in the Selected Objects section. For more information, see Map object names. To remove one or more objects that are selected for migration, click the objects in the Selected Objects section and then click the icon to move the objects to the Source Objects section. Note If you use the object name mapping feature to rename an object, other objects that depend on the object may fail to be migrated. To specify WHERE conditions to filter data, right-click a table in the Selected Objects section. In the dialog box that appears, specify the conditions. For more information, see Specify filter conditions. To select the SQL operations for incremental migration, right-click an object in the Selected Objects section. In the dialog box that appears, select the SQL operations that you want to migrate.

Click Next: Advanced Settings to configure advanced settings.

Configuration	Description
Dedicated Cluster for Task Scheduling	By default, DTS schedules the data migration task to the shared cluster if you do not specify a dedicated cluster. If you want to improve the stability of data migration tasks, purchase a dedicated cluster. For more information, see What is a DTS dedicated cluster.
Retry Time for Failed Connections	The retry time range for failed connections. If the source or destination database fails to be connected after the data migration task is started, DTS immediately retries a connection within the retry time range. Valid values: 10 to 1,440. Unit: minutes. Default value: 720. We recommend that you set the parameter to a value greater than 30. If DTS is reconnected to the source and destination databases within the specified retry time range, DTS resumes the data migration task. Otherwise, the data migration task fails. Note If you specify different retry time ranges for multiple data migration tasks that share the same source or destination database, the value that is specified later takes precedence. When DTS retries a connection, you are charged for the DTS instance. We recommend that you specify the retry time range based on your business requirements. You can also release the DTS instance at the earliest opportunity after the source database and destination instance are released.
Retry Time for Other Issues	The retry time range for other issues. For example, if DDL or DML operations fail to be performed after the data migration task is started, DTS immediately retries the operations within the retry time range. Valid values: 1 to 1440. Unit: minutes. Default value: 10. We recommend that you set the parameter to a value greater than 10. If the failed operations are successfully performed within the specified retry time range, DTS resumes the data migration task. Otherwise, the data migration task fails. Important The value of the Retry Time for Other Issues parameter must be smaller than the value of the Retry Time for Failed Connections parameter.
Enable Throttling for Full Data Migration	Specifies whether to enable throttling for full data migration. During full data migration, DTS uses the read and write resources of the source and destination databases. This may increase the loads of the database servers. You can enable throttling for full data migration based on your business requirements. To configure throttling, you must configure the Queries per second (QPS) to the source database, RPS of Full Data Migration, and Data migration speed for full migration (MB/s) parameters. This reduces the loads of the destination database server. Note You can configure this parameter only if you select Full Data Migration for the Migration Types parameter.
Enable Throttling for Incremental Data Migration	Specifies whether to enable throttling for incremental data migration. To configure throttling, you must configure the RPS of Incremental Data Migration and Data migration speed for incremental migration (MB/s) parameters. This reduces the loads of the destination database server. Note You can configure this parameter only if you select Incremental Data Migration for the Migration Types parameter.
Whether to delete SQL operations on heartbeat tables of forward and reverse tasks	Specifies whether to write SQL operations on heartbeat tables to the source database while the DTS instance is running. Valid values: Yes: does not write SQL operations on heartbeat tables. In this case, a latency of the DTS instance may be displayed. No: writes SQL operations on heartbeat tables. In this case, features such as physical backup and cloning of the source database may be affected.
Environment Tag	If needed, you can select an environment tag to identify the instance. In this example, you do not need to select a tag.
Monitoring and Alerting	Specifies whether to configure alerting for the data migration task. If the task fails or the migration latency exceeds the specified threshold, the alert contacts receive notifications. Valid values: No: does not configure alerting. Yes: configures alerting. In this case, you must also configure the alert threshold and alert notification settings. For more information, see the Configure monitoring and alerting when you create a DTS task section of the Configure monitoring and alerting topic.

Click Next Step: Data Verification to configure the data verification task.
For more information about how to use the data verification feature, see Configure a data verification task.

Save the task settings and run a precheck.
- To view the parameters to be specified when you call the relevant API operation to configure the DTS task, move the pointer over Next: Save Task Settings and Precheck and click Preview OpenAPI parameters.
- If you do not need to view or have viewed the parameters, click Next: Save Task Settings and Precheck in the lower part of the page.
Note
- Before you can start the data migration task, DTS performs a precheck. You can start the data migration task only after the task passes the precheck.
- If the task fails to pass the precheck, click View Details next to each failed item. After you analyze the causes based on the check results, troubleshoot the issues. Then, run a precheck again.
- If an alert is triggered for an item during the precheck:
  If an alert item cannot be ignored, click View Details next to the failed item and troubleshoot the issues. Then, run a precheck again.
  If the alert item can be ignored, click Confirm Alert Details. In the View Details dialog box, click Ignore. In the message that appears, click OK. Then, click Precheck Again to run a precheck again. If you ignore the alert item, data inconsistency may occur, and your business may be exposed to potential risks.

Purchase the instance.

Wait until Success Rate becomes 100%. Then, click Next: Purchase Instance.

On the Purchase Instance page, configure the Instance Class parameter for the data migration instance. The following table describes the parameters.

Section	Parameter	Description
New Instance Class	Resource Group	The resource group to which the data migration instance belongs. Default value: default resource group. For more information, see What is Resource Management?
New Instance Class	Instance Class	DTS provides instance classes that vary in the migration speed. You can select an instance class based on your business scenario. For more information, see Instance classes of data migration instances.

Read and agree to Data Transmission Service (Pay-as-you-go) Service Terms by selecting the check box.
Click Buy and Start. In the message that appears, click OK.
You can view the progress of the task on the Data Migration page.
Note
- If a data migration task cannot be used to migrate incremental data, the task automatically stops. The Completed is displayed in the Status section.
- If a data migration task can be used to migrate incremental data, the task does not automatically stop. The incremental data migration task never stops or completes. The Running is displayed in the Status section.