Use DTS to migrate data from PolarDB-X 2.0 to MaxCompute - Data Transmission Service

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

Prerequisites

Activate MaxCompute and create a MaxCompute project. For more information, see Activate MaxCompute and Create a MaxCompute project.
Configure the MaxCompute whitelist to allow DTS to access MaxCompute. For more information, see Configure a whitelist for Alibaba Cloud services to access MaxCompute.
An AccessKey pair is created for the Alibaba Cloud account that owns the destination MaxCompute project. For more information, see Create an AccessKey pair.
Note
You can Create a RAM user and Set a RAM user as the super administrator for a MaxCompute project.

Notes

Type	Description
Source database limits	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. The source database does not support read-only instances of Enterprise Edition PolarDB-X 2.0. 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. If you want 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 both full data migration and incremental data migration, the binary logs of the source database must be stored for at least seven days. After full data migration is complete, you can set the retention period to more than 24 hours. Otherwise, DTS may fail to obtain the binary logs and the task may fail. In exceptional circumstances, data inconsistency or loss may occur. Make sure that you set the retention period of binary logs in accordance with the preceding requirements. Otherwise, the SLA of DTS does not guarantee service reliability and performance. Operational limits on the source database: During schema migration and full data migration, do not perform DDL operations to change the schemas of databases or tables. Otherwise, the data migration task fails. During full and incremental migration, DTS temporarily disables constraint checks and foreign key cascade operations at the session level. If cascade update or delete operations occur in the source database while the task is running, data inconsistency may occur. If you want to change the network type of the PolarDB-X 2.0 instance during data migration, you must also modify the network connection settings of the data migration task. If you perform only full data migration, do not write data to the source database during data migration. Otherwise, data will be inconsistent between the source and destination databases. To ensure data consistency, we recommend that you select schema migration, full data migration, and incremental data migration as the migration types. The data migration instance does not support the TABLEGROUP and the database or schema that contains Locality attribute. Migration of tables whose names are reserved words, such as `select`, is not supported.
Other limits	Evaluate the performance of the source and destination databases before you start data migration. Perform data migration during off-peak hours. Full data migration consumes read and write resources on the source and destination databases, which can increase the database load. DTS attempts to resume failed migration tasks that are created within the last seven days. Therefore, before you switch your business to the destination 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 destination instance. This prevents data in the destination instance from being overwritten by data from the source database after the task is automatically resumed. 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.
Other notes	DTS periodically updates the `dts_health_check`.`ha_health_check` table in the source database to advance the binary log offset.

Billing

Migration type	Task configuration fee	Internet traffic fee
Schema migration and full data migration	Free of charge	No fees are charged in this example. Note If the Access Method parameter of the destination database is set to Public IP Address, you are charged for internet traffic fees. For more information, see Billing overview.
Incremental data migration	Charged. For more information, see Billing overview.

Migration types

Schema migration
DTS migrates the schemas of the required objects from the source database to MaxCompute. During schema synchronization, DTS adds the _base suffix to the end of the source table name. For example, if the name of the source table is customer, the name of the table in MaxCompute is customer_base.
Full data migration
DTS migrates the historical data of the table from the source database to the destination table in MaxCompute. For example, the customer table in the source database is migrated to the customer_base table in MaxCompute. The data is the basis for subsequent incremental synchronization.
Note
The destination table that is suffixed with _base is known as a full baseline table.
Incremental migration
DTS creates an incremental log table in MaxCompute. The table name is in the format of `DestinationTableName_log`, such as `customer_log`. Then, DTS migrates incremental data from the source database to this table in real time.
Note
For more information about the structure of the incremental log table, see Incremental log table structure.

SQL operations supported by incremental migration

Operation type	SQL statement
DML	INSERT, UPDATE, DELETE
DDL	ADD COLUMN Note The ADD COLUMN operation that contains attribute columns cannot be migrated.

Permissions required for the database accounts

Database	Schema migration	Full migration	Incremental migration
PolarDB-X 2.0 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.
MaxCompute	Read and write permissions

Data type mappings

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

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.

Warning

After you select the source and destination instances, we recommend that you carefully read the Limits at the top of the page to ensure that the migration task can be created and run successfully.

Category	Configuration	Description
N/A	Task Name	DTS automatically generates a task name. Specify a descriptive name for easy identification. The name does not need to be unique.
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 Cloud Instance.
	Instance Region	Select the region where the source PolarDB-X 2.0 instance resides.
	Cross-account	This example shows how to migrate data between instances that belong to 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 of the source PolarDB-X 2.0 instance. For information about the required permissions, see Permissions required for the database accounts.
	Database Password	Enter the password for the database account.
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 MaxCompute.
	Access Method	Select Cloud Instance.
	Instance Region	Select the region where the destination MaxCompute project resides.
	Project	Enter the name of the destination MaxCompute project.
	AccessKey ID of Alibaba Cloud Account	Enter the AccessKey pair that you prepared in the Prerequisites section.
	AccessKey Secret of Alibaba Cloud Account

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.
Click OK to grant permissions to the MaxCompute account.

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 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 you do not select Schema Migration, make sure a database and a table are created in the destination database to receive data and the object name mapping feature is enabled in Selected Objects. 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.
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.
Additional Column Rule	When DTS migrates data to MaxCompute, it adds some additional columns to the destination tables. If the names of the additional columns conflict with existing columns in the destination tables, the data migration fails. Select New Rule or Old Rule as needed. Warning Before you select an additional column rule, evaluate whether the names of the additional columns will conflict with existing columns in the destination tables.
Partition Definition of Incremental Data Table	Select a partition name as needed. For more information about partitions, see Partitions.
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 make sure 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 objects to migrate at the table level.
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, the migration of other objects that depend on the mapped object may fail. To filter data using a WHERE clause, right-click the source table in the Selected Objects box and set a filter condition in the dialog box that appears. To select the 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 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	You can select an environment tag to identify the instance. In this example, you do not need to select a tag.
Configure ETL	Specifies whether to enable 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.
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.

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.

Incremental log table structure

Note

You must run set odps.sql.allow.fullscan=true; in MaxCompute to set the project property to allow full table scans.

When DTS migrates incremental data from the source database to the incremental log table in MaxCompute, it stores the metadata described in the following table in addition to the incremental data and incremental log table partitions.

Field	Description
record_id	The ID of the incremental log record. This ID uniquely identifies the log. Note The ID value is unique and incremental. If the operation type of the incremental log is UPDATE, the incremental update is split into two records that record the values before and after the update. The two records have the same record_id.
operation_flag	The operation type. Valid values: I: INSERT operation. D: DELETE operation. U: UPDATE operation.
utc_timestamp	The operation timestamp, which is the timestamp of the binary log in UTC.
before_flag	Indicates whether all column values are the values before the update. Valid values: Y and N.
after_flag	Indicates whether all column values are the values after the update. Valid values: Y and N.