Migrate data from a PolarDB-X 2.0 instance to a MaxCompute project - Data Transmission Service

This topic describes how to migrate data from a PolarDB-X 2.0 instance to a MaxCompute project by using Data Transmission Service (DTS).

Prerequisites

A PolarDB-X 2.0 instance is created. For more information, see Create a PolarDB-X instance.
MaxCompute is activated and a MaxCompute project is created. For more information, see Activate MaxCompute and DataWorks and Create a MaxCompute project.

Limits

Category	Description
Limits on the source database	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 configure multiple tasks to migrate the tables in batches or configure a task to migrate the entire database. If you need to migrate incremental data, make sure that the following requirements are met: The binary logging feature is enabled. The value of the binlog_row_image parameter is set to full. Otherwise, error messages are returned during precheck and the data migration task cannot be started. If you perform only incremental data migration, the binary logs of the source database must be stored for more than 24 hours. If you perform full data migration and incremental data migration, the binary logs of the source database must be stored for at least seven days. Otherwise, Data Transmission Service (DTS) may fail to obtain the binary logs and the task may fail. In exceptional circumstances, data inconsistency or loss may occur. After full data migration is complete, you can set the retention period to more than 24 hours. Make sure that you set the retention period of binary logs based on the preceding requirements. Otherwise, the Service Level Agreement (SLA) of DTS does not guarantee service reliability or performance. Limits on operations: During data migration, do not upgrade or downgrade the source database, migrate frequently-updated tables, change shard keys, or perform DDL operations on the objects to be migrated. Otherwise, the data migration task fails. During full data migration and incremental data migration, DTS temporarily disables the constraint check and cascade operations on foreign keys at the session level. If you perform the cascade and delete operations on the source database during data migration, data inconsistency may occur. If you want to switch the network type of the PolarDB-X 2.0 instance during data migration, modify the network information about the data migration instance after the network type is switched. If you perform only full data migration, do not write data to the source database during data migration. Otherwise, data inconsistency occurs. To ensure data consistency, we recommend that you select schema migration, full data migration, and incremental data migration as the migration types.
Other limits	Before you migrate data, evaluate the impact of data migration on the performance of the source and destination databases. We recommend that you migrate data during off-peak hours. During full data migration, DTS uses the read and write resources of the source and destination databases. This may increase the loads on the database servers. DTS attempts to resume data migration tasks that failed within the last seven days. Before you switch workloads to the destination instance, stop or release the data migration task. You can also execute the `REVOKE` statement to revoke the write permissions from the accounts that are used by DTS to access the destination instance. Otherwise, the data in the source database will overwrite the data in the destination instance after the failed task is resumed.
Usage notes	DTS updates the `dts_health_check`.`ha_health_check` table in the source database as scheduled to move forward the binary log file position.

Billing

Migration type	Task configuration fee	Internet traffic fee
Schema migration and full data migration	Free of charge.	Free of charge.
Incremental data migration	Charged. For more information, see Billing overview.	Free of charge.

Migration types

Schema migration
DTS migrates the schemas of objects from the source database to the destination database.
Full data migration
DTS migrates the existing data of objects from the source database to the destination database.
Incremental data migration
After full data migration is complete, DTS migrates incremental data from the source database to the destination database. Incremental data migration allows data to be migrated smoothly without interrupting the services of self-managed applications during data migration.

SQL operations that support incremental data migration

Operation type	SQL statement
DML	INSERT, UPDATE, and DELETE

Permissions required for database accounts

Database	Schema migration	Full data migration	Incremental data migration
PolarDB-X instance	The SELECT permission	The SELECT permission	The REPLICATION SLAVE and REPLICATION CLIENT permissions, and the SELECT permission on the objects to be migrated Note For more information about how to grant the permissions to the database account, see Data synchronization tools for PolarDB-X.
MaxCompute	Read and write permissions

Data type mappings

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

Procedure

Go to the Data Migration Tasks page.
1. Log on to the Data Management (DMS) console.
2. In the top navigation bar, click DTS.
3. In the left-side navigation pane, choose DTS (DTS) > Data Migration.
Note
- Operations 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.
- You can also go to the Data Migration Tasks page of the new DTS console.
From the drop-down list next to Data Migration Tasks, select the region in which the data migration instance resides.
Note If you use the new DTS console, you must select the region in which the data migration instance resides in the upper-left corner.

Click Create Task. On the page that appears, configure the source and destination databases.

Warning After you select the source and destination instances, we recommend that you read the Limits section that is displayed in the upper part of the page. This helps you create and run the data migration task.

Section	Parameter	Description
N/A	Task Name	The task name that DTS automatically generates. We recommend that you specify a descriptive name that makes it easy to identify. You do not need to specify a unique task name.
Source Database	Select an existing DMS database instance	The database instance that you want to use. You can choose whether to select an existing instance based on your business requirements. If you select an existing instance, DTS automatically populates the parameters for the database. If you do not select an existing instance, you must manually configure parameters for the database.
	Database Type	The type of the source database. Select PolarDB-X 2.0.
	Access Method	The access method of the source database. Select Alibaba Cloud Instance.
	Instance Region	The region in which the source PolarDB-X 2.0 instance resides.
	Replicate Data Across Alibaba Cloud Accounts	Specifies whether to migrate data across Alibaba Cloud accounts. In this example, No is selected.
	Instance ID	The ID of the source PolarDB-X 2.0 instance.
	Database Account	The username of the database account of the source PolarDB-X 2.0 instance. For information about the permissions that are required for the account, see the Permissions required for database accounts section of this topic.
	Database Password	The password of the database account.
Destination Database	Select an existing DMS database instance	The database instance that you want to use. You can choose whether to select an existing instance based on your business requirements. If you select an existing instance, DTS automatically populates the parameters for the database. If you do not select an existing instance, you must manually configure parameters for the database.
	Database Type	The type of the destination database. Select MaxCompute.
	Access Method	The access method of the destination database. Select Alibaba Cloud Instance.
	Instance Region	The region in which the destination MaxCompute project resides.
	Project	The name of the MaxCompute project.
	AccessKey ID of Alibaba Cloud Account	The AccessKey ID of the account that you use to connect to the destination MaxCompute project. For more information, see Create an AccessKey pair.
	AccessKey Secret of Alibaba Cloud Account	The AccessKey secret of the account that you use to connect to the destination MaxCompute project. For more information, see Create an AccessKey pair.

In the lower part of the page, click Test Connectivity and Proceed.
If the source or destination database is an Alibaba Cloud database instance, such as an ApsaraDB RDS for MySQL or ApsaraDB for MongoDB instance, DTS automatically adds the CIDR blocks of DTS servers to the IP address whitelist of the instance. If the source or destination database is a self-managed database hosted on an Elastic Compute Service (ECS) instance, DTS automatically adds the CIDR blocks of DTS servers to the security group rules of the ECS instance, and you must make sure that the ECS instance can access the database. If the self-managed database is hosted on multiple ECS instances, you must manually add the CIDR blocks of DTS servers to the security group rules of each ECS instance. If the source or destination database is a self-managed database that is deployed in a data center or provided by a third-party cloud service provider, you must manually add the CIDR blocks of DTS servers to the IP address whitelist of the database to allow DTS to access the database. For more information, see the "CIDR blocks of DTS servers" section of the Add the CIDR blocks of DTS servers to the security settings of on-premises databases topic.
Warning
If the public CIDR blocks of DTS servers are automatically or manually added to the IP address whitelist of a database instance or to the security group rules of an ECS instance, security risks may arise. Therefore, before you use DTS to migrate data, you must understand and acknowledge the potential risks and take preventive measures, including but not limited to the following measures: enhancing the security of your account and password, limiting the ports that are exposed, authenticating API calls, regularly checking the IP address whitelist or ECS security group rules and forbidding unauthorized CIDR blocks, and connecting the database to DTS by using Express Connect, VPN Gateway, or Smart Access Gateway.
Click OK to grant permissions to your MaxCompute account.

Configure the objects to be migrated and advanced settings.

Parameter	Description
Migration Types	If you want to perform only full data migration, select Schema Migration and Full Data Migration. To ensure service continuity during data migration, select Schema Migration, Full Data Migration, and Incremental Data Migration. Note If Schema Migration is selected, the foreign keys in the source database are also migrated to the destination database. If Full Data Migration is selected, you can migrate the schema and data in the tables that are created by executing the CREATE TABLE statement to the destination database. If Incremental Data Migration is not selected, 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.
Processing Mode of Conflicting Tables	Precheck and Report Errors: checks whether the destination database contains tables that have 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 You can use the object name mapping feature to rename the tables that are migrated to the destination database. You can use this feature if the source and destination databases contain tables that have identical table names and the tables in the destination database cannot be deleted or renamed. 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 schemas, DTS does not migrate data records that have the same primary key values as data records in the destination database. If the source and destination databases have different schemas, only specific columns are migrated or the data migration task fails. Proceed with caution.
Naming Rules of Additional Columns	If you migrate data to a MaxCompute project, DTS adds additional columns to the destination table. If the names of additional columns are the same as the names of existing columns in the destination table, data migration fails. You can select New Rule or Previous Rule based on your business requirements. Warning Before you specify this parameter, check whether additional columns have the same names as the existing columns in the destination table.
Partition Definition of Incremental Data Table	Select the partition names based on your business requirements. For more information, see Partition.
Capitalization of Object Names in Destination Instance	The capitalization of database names, table names, and column names in the destination instance. By default, DTS default policy is selected. You can select other options to ensure that the capitalization of object names is consistent with that of the source or destination database. For more information, see Specify the capitalization of object names in the destination instance.
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 You can select columns, tables, or databases as the objects to be migrated. If you select tables as the objects to be migrated, DTS does not migrate other objects such as views, triggers, or stored procedures to the destination database. If you select a database as the object to be migrated, DTS migrates data based on the following default rules: If the table to be migrated in the source database has a primary key, such as a single-column primary key or a composite primary key, the primary key columns are specified as the distribution keys. If the table to be migrated in the source database does not have a primary key, an auto-increment primary key column is automatically generated in the destination table. This may cause data inconsistency between the source and destination databases.
Selected Objects	To rename an object that you want to migrate to the destination instance, right-click the object in the Selected Objects section. For more information, see Map the name of a single object. To rename multiple objects at a time, click Batch Edit in the upper-right corner of the Selected Objects section. For more information, see Map multiple object names at a time. Note If you use the object name mapping feature to rename an object, other objects that are dependent 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 Use SQL conditions to filter data. To select the SQL operations performed on a specific database or table, right-click an object in the Selected Objects section. In the dialog box that appears, select the SQL operations that you want to migrate. For more information, see the SQL operations that support incremental data migration section of this topic.

Click Next: Advanced Settings to configure advanced settings.

Parameter	Description
Set Alerts	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 will receive notifications. Valid values: No: does not configure alerting. Yes: configures alerting. If you select Yes, you must also specify the alert threshold and alert contacts. For more information, see Configure monitoring and alerting.
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 time range. Valid values: 10 to 1440. Unit: minutes. Default value: 720. We recommend that you set the parameter to a value greater than 30. If DTS reconnects to the source and destination databases within the specified time range, DTS resumes the data migration task. Otherwise, the data migration task fails. Note If you set different retry time ranges for multiple data migration tasks that have the same source or destination database, the shortest retry time range that is set 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 your earliest opportunity after the source and destination instances are released.
The wait time before a retry when other issues occur in the source and destination databases	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 The wait time before a retry when other issues occur in the source and destination databases parameter must be smaller than the value of the Retry Time for Failed Connections parameter.
Configure ETL	Specifies whether to configure the extract, transform, and load (ETL) feature. For more information, see What is ETL?. Valid values: Yes: configures the ETL feature. You can enter data processing statements in the code editor. For more information, see Configure ETL in a data migration or data synchronization task. No: does not configure the ETL feature.
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 when the DTS instance is running. Yes: does not write SQL operations on heartbeat tables. In this case, 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.

In the lower part of the page, click Next: Save Task Settings and Precheck.
You can move the pointer over Next: Save Task Settings and Precheck and click Preview OpenAPI parameters to view the parameters to be specified when you call the relevant API operation to configure the DTS task.
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 troubleshoot the issues based on the error message, you can run a precheck again.
- If an alert is triggered for an item during the precheck:
  If the 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.
Wait until the 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 Specifications 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 to start the data migration task. You can view the progress of the task in the task list.