How to migrate data between PolarDB-X 2.0 instances-Data Transmission Service(DTS)-阿里云帮助中心

Prerequisites

You have created the source and destination PolarDB-X 2.0 instances.
The storage capacity of the destination PolarDB-X 2.0 instance must exceed the storage space used by the source PolarDB-X 2.0 instance.

Limitations

Note

During a schema migration, DTS migrates foreign keys from the source database to the destination database.
During full and incremental data 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 occur.

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. If a table name in the PolarDB-X 2.0 instance contains uppercase letters, DTS supports only schema migration for that table. 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. 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.
Other limitations	Before you start the data migration, evaluate the performance of the source and destination databases. Perform data migration during off-peak hours. During full data migration, DTS consumes read and write resources on both the source and destination databases, which increases the database load. During full data migration, concurrent INSERT operations can cause table fragmentation in the destination database. As a result, tables in the destination database may occupy more storage space than those in the source database. DTS attempts to recover failed tasks for up to seven days. Therefore, before you switch your business to the destination database, make sure to end or release the task. Alternatively, revoke the write permissions of the account used by DTS to access the destination database with the `REVOKE` command. This prevents DTS from overwriting data in the destination database if the task is automatically recovered. 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	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
DDL	ALTER TABLE CREATE FUNCTION, CREATE INDEX, CREATE TABLE Note If the source database is an Enterprise Edition PolarDB-X 2.0 instance, `CREATE FUNCTION` and `CREATE INDEX` operations are not migrated. DROP INDEX, DROP TABLE RENAME TABLE Note The `RENAME TABLE` operation may cause data inconsistency. For example, if you select only one table for migration and then rename it in the source instance, data from that table is not migrated. To avoid this issue, select the entire database to which the table belongs as the migration object. Make sure that the database that contains the table both before and after the rename operation is included in the migration objects. TRUNCATE TABLE

Required permissions for database accounts

Database	Schema migration	Full data migration	Incremental data migration
Source PolarDB-X 2.0 instance	SELECT permission	SELECT permission	REPLICATION SLAVE and REPLICATION CLIENT permissions, and SELECT permission on the objects to be migrated. Note For more information about how to grant permissions, see Account permission issues during data synchronization.
Destination PolarDB-X 2.0 instance	Read and write 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.

Warning

After you select the source and destination instances, we recommend that you carefully read the limits displayed at the top of the page. Otherwise, the task may fail or data inconsistency may occur.

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.
	Connection Type	Select Alibaba Cloud Instance.
	Instance Region	Select the region where the source PolarDB-X 2.0 instance resides.
	Replicate Data Across Alibaba Cloud Accounts	This topic uses a migration within the same Alibaba Cloud account as an example. 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 Required permissions 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 PolarDB-X 2.0.
	Connection Type	Select Alibaba Cloud Instance.
	Instance Region	Select the region where the destination PolarDB-X 2.0 instance resides.
	Instance ID	Select the ID of the destination PolarDB-X 2.0 instance.
	Database Account	Enter the database account of the destination PolarDB-X 2.0 instance. For more information about the required permissions, see Required permissions for database accounts.
	Database Password	Enter the password for the database account.

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	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 for Existing Destination 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.
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 The granularity for selecting migration objects is schema, table, and column. If you select only tables or columns as migration objects, other objects 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 may fail. To set a WHERE clause to filter data, right-click the table to be migrated in the Selected Objects box, and then set the filter condition in the dialog box that appears. For more information about how to set the condition, see Filter data by using SQL statements. To select the SQL operations to migrate at the database or table level, right-click the migration object in the Selected Objects box, and then 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 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. No selection is required for this example.
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.
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.

Click Next: Data Validation to configure a data validation task.

For more information about the data validation feature, see Configure data validation.

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.