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

Prerequisites

The storage for the source PolarDB-X 1.0 instance must be an ApsaraDB RDS for MySQL instance, which includes privately customized RDS instances and separately purchased RDS instances. PolarDB for MySQL is not supported.
You have created a destination PolarDB-X 2.0 instance and a database to store the migrated data. For more information, see Create an instance (Starter Edition) and Create a database.
The available storage space of the destination instance must be larger than the storage space used by the source instance.

Limitations

Note

DTS migrates foreign keys during schema migration.
During full and incremental data migration, DTS temporarily disables constraint checks and foreign key cascades at the session level. Cascade updates or deletes on the source database while the task runs may cause data inconsistency.

Type	Description
Source database limitations	The tables to be migrated must have a primary key or a unique constraint. Otherwise, data duplication may occur in the target database. Schema migration is not supported for tables that have only a unique constraint. We recommend using a primary key. If you migrate data at the table level and need to edit tables, such as by mapping table or column names, a single data migration task supports a maximum of 1,000 tables. If you exceed this limit, the task submission fails. In this case, we recommend splitting the tables into multiple tasks or migrating the entire database. For the binary log of the ApsaraDB RDS for MySQL instance that is attached to PolarDB-X 1.0: By default, the binary log is enabled. See View instance parameters and confirm that the `binlog_row_image` parameter is set to `full`. Otherwise, the precheck fails and the data migration task cannot start. For an incremental data migration task, DTS requires the source database to retain its local binary log for at least 24 hours. For a task that includes both full data migration and incremental data migration, DTS requires the source database to retain its local binary log for at least 7 days. You can change the retention period to 24 hours or more after the full data migration is complete. If the retention period is insufficient, DTS may fail to obtain the binary log. This can cause the task to fail and, in extreme cases, lead to data inconsistency or loss. Issues caused by an insufficient binary log retention period are not covered by the SLA. Operational restrictions on the source database: During data migration, do not perform scale-out, scale-in, hot table migration, shard key changes, or DDL changes. Otherwise, the data migration task fails. Note During the full migration phase, DTS queries the source database. This creates 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 on the source database while the task is running, data inconsistency may occur. If you perform only a full data migration, do not write new data to the source database. Otherwise, data inconsistency will occur between the source and destination databases. To maintain real-time data consistency, select schema migration, full data migration, and incremental data migration. The source PolarDB-X 1.0 instance must be version 5.2 or later. Do not change the type of a broadcast table in the source PolarDB-X 1.0 instance while a DTS migration task is running (for example, from a broadcast table to a single table or a sharded table). If you need to change the table type, stop the migration task. After the change is complete, reconfigure the migration task.
Other limitations	The storage for PolarDB-X 1.0 must be ApsaraDB RDS for MySQL, including private custom RDS instances and separately purchased RDS instances. PolarDB for MySQL is not supported as the storage type. A data migration task for PolarDB-X 1.0 is a distributed task. DTS creates a sub-task for each ApsaraDB RDS for MySQL instance attached to the PolarDB-X 1.0 instance. You can view the status of sub-tasks on the performance monitoring page. DTS relies on the continuity of XA transactions in the source PolarDB-X 1.0 instance to ensure data consistency for incremental migration tasks. If the continuity of XA transactions is broken, for example, during a disaster recovery scenario for the incremental data capture module, uncommitted XA transactions may be lost. Before you migrate data, evaluate the performance of the source and target databases. We also recommend performing data migration during off-peak hours. Otherwise, DTS consumes read and write resources on both the source and target databases during full data migration, which may increase the database load. During full data migration, DTS runs concurrent INSERT operations, which can cause table fragmentation in the target database. As a result, tables in the target database may occupy more storage space than in the source instance. Verify that the migration precision for columns of the FLOAT or DOUBLE data type meets your business requirements. DTS reads the values of these columns by using the `ROUND(COLUMN,PRECISION)` function. If the precision is not explicitly defined, DTS migrates FLOAT columns with a precision of 38 digits and DOUBLE columns with a precision of 308 digits. DTS attempts to resume a failed task within seven days. Therefore, before the cutover to the target instance, you must end or release the task. Alternatively, revoke the write permissions from the DTS account by using the `revoke` command. This prevents the source data from overwriting data in the target instance if the task automatically resumes. 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.

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

Database account permissions

Database	Schema migration	Full data migration	Incremental data migration	Authorization
PolarDB-X 1.0 instance	SELECT	SELECT	REPLICATION SLAVE, REPLICATION CLIENT, and SELECT on the objects to migrate. DTS grants these permissions automatically.	Manage accounts
PolarDB-X 2.0 instance	Read and write permissions			Manage accounts

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.

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	Database Type	Select PolarDB-X 1.0.
	Connection Type	Select Alibaba Cloud Instance.
	Instance Region	Select the region of the source PolarDB-X 1.0 instance.
	Replicate Data Across Alibaba Cloud Accounts	This example shows a migration within the same Alibaba Cloud account. Select No.
	Instance ID	Select the ID of the source PolarDB-X 1.0 instance.
	Database Account	Enter the database account of the source PolarDB-X 1.0 instance.
	Database Password	Enter the password for the specified database account.
Destination Database	Database Type	Select PolarDB-X 2.0.
	Connection Type	Select Alibaba Cloud Instance.
	Instance Region	Select the region of the destination PolarDB-X 2.0 instance.
	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.
	Database Password	Enter the password for the specified 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
Synchronization Type	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.
Case Policy for Destination Object Names	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	In the Source Objects box, click the objects to migrate, and then click to move them to the Selected Objects box. Note Select objects to migrate at the table level. If you select an entire database, any changes to add or delete tables in that database will not be migrated to the destination.
Selected Objects	To change the name of a single migration object in the destination instance, right-click the object in the Selected Objects box. For more information about how to set the name, see Map a single table or column name. To change the names of multiple migration objects in a batch, click Batch Edit in the upper-right corner of the Selected Objects box. For more information about how to set the names, see Map multiple table or column names in a batch. Note If you use the object name mapping feature, other objects that depend on the mapped object may fail to migrate.

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. This is not required 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 notifications. 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 migration task.

When the Success Rate reaches 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.