Migrate from Db2 for LUW to PolarDB-X 2.0-Data Transmission Service(DTS)-阿里云帮助中心

Prerequisites

You have created the source Db2 for LUW database and the destination PolarDB-X 2.0 instance.

Note
For more information about supported database versions, see Overview of migration solutions.
The destination instance must have more available storage space than the total data size of the source database.

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.

Category	Description
Source database limits	Bandwidth: The source database server must have sufficient outbound bandwidth. Insufficient bandwidth slows the migration. Tables to be migrated must have primary keys or UNIQUE constraints with unique field values. Otherwise, the destination database may contain duplicate data. If you migrate at the table level with edits such as column name mapping, a single task supports up to 1,000 tables. Exceeding this limit causes a request error. Split the tables into multiple tasks or migrate the entire database instead. Incremental migration requires the following data log settings: Data logging must be enabled. Otherwise, the precheck fails and blocks the task from starting. DTS requires source data logs to be retained for more than 24 hours for incremental migration, or at least 7 days for full-plus-incremental migration. After full migration completes, you can reduce the retention to more than 24 hours. If retention is too short, DTS may fail to read data logs, causing task failure or, in extreme cases, data inconsistency or loss. Issues caused by insufficient log retention are not covered by the DTS SLA. Limits on operations in the source database: During full migration, do not perform DDL operations that change database or table schemas. Otherwise, the task fails. If you perform only full data migration, do not write new data to the source instance. Otherwise, data inconsistency occurs between the source and destination databases. To maintain real-time consistency, select both full and incremental migration. The Change Data Capture (CDC) property must be enabled for the tables to be migrated.
Other limits	DTS migrates incremental data from a Db2 for LUW database to the destination database based on the CDC replication technology of Db2 for LUW. However, CDC replication has its own limits. General data restrictions for SQL Replication. Evaluate source and destination database performance before starting migration. Migrate during off-peak hours because full migration consumes read and write resources on both databases, increasing load. Full migration uses concurrent INSERT operations that cause table fragmentation. After full migration, tables in the destination database use more storage space than in the source. Verify that the DTS migration precision for FLOAT or DOUBLE columns meets your requirements. DTS reads these columns using the `ROUND(COLUMN,PRECISION)` function. Default precision: 38 for FLOAT, 308 for DOUBLE. DTS attempts to recover failed tasks for up to seven days. Before switching your workload to the destination instance, stop or release the task. Alternatively, use the `revoke` command to revoke write permissions from the DTS account on the destination instance. This prevents a recovered task from overwriting destination data. 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. If the destination PolarDB-X 2.0 table has auto partitioning enabled (`auto_partition=true`), each DDL statement executed on the source can contain only one `alter_specification`. Otherwise, DTS reports an error (`TDDL-4998`: `Multi alter specifications when create GSI not support yet`). To execute a DDL statement that contains multiple `alter_specification` items, split each `alter_specification` into a separate DDL statement and execute them one by one. For more information, see ALTER TABLE (DRDS mode) and ALTER TABLE (AUTO mode).
Special cases	Because the source Db2 for LUW database is self-managed: If a primary/secondary switchover occurs on the source database during migration, the migration task fails. DTS calculates migration latency by comparing the timestamp of the last migrated entry with the current time. If no DML operations run on the source for a long time, the displayed latency may be inaccurate. To update it, perform a DML operation on the source database. Note For full database migration, you can create a heartbeat table that receives writes at regular intervals (for example, every second) to keep latency readings accurate.

Migration types

Schema migration

Data Transmission Service (DTS) migrates the schema definitions of the migration objects from the source database to the destination database.
- DTS supports schema migration for tables, views, triggers, stored procedures, and functions.
  
  Note
  The routine_body of stored procedures, the routine_body of functions, and the select_statement of views are not modified.
- During schema migration, DTS changes the `DEFINER` to `INVOKER` for the views, stored procedures, and functions to be migrated. This action changes the value of `SQL SECURITY` to `INVOKER`. DTS also sets the `DEFINER` to the destination database account that is used for the migration task.
  
  Note
  The security authentication method and definer of the source database are not modified.
- Because DTS does not migrate user information, you must grant read and write permissions to the invoker to call views, stored procedures, and functions in 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, and DELETE

Required database account permissions

Database	Schema and full data migration	Incremental data migration	Actions
Db2 for LUW	CONNECT and SELECT permissions	DBADM authority	Create User and Authorities overview
PolarDB-X 2.0 instance	Read and write permissions on the destination database	Read and write permissions on the destination database	Account management

Preparations

To perform incremental data migration, you must enable archive logging for the Db2 for LUW database. For more information, see Primary log archive method and Secondary log archive method.

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.

Section	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 DB2 for LUW.
	Access Method	Select Public IP Address.
	Instance Region	Select the region where the source Db2 for LUW database resides.
	Domain Name or IP Address	Enter the connection endpoint of the source Db2 for LUW database. In this example, enter the public IP address.
	Port Number	Enter the service port of the source Db2 for LUW database. The port must be accessible over the internet. The default port is 50000.
	Database Name	Enter the name of the database in the source Db2 for LUW instance that contains the migration objects.
	Database Account	Enter the account for the source Db2 for LUW database. For the required permissions, see Required database account permissions.
	Database Password	Enter the password for the database account.
	Connection Method	Select Non-encrypted or SSL-encrypted based on your database requirements. If you set this parameter to SSL-encrypted, you must enable SSL encryption for the RDS for MySQL instance beforehand. For more information, see Quickly enable SSL encryption using a cloud certificate.
Destination Database	Database Type	Select PolarDB-X 2.0.
	Access Method	Select Alibaba Cloud Instance.
	Instance Region	Select the region where the destination PolarDB-X 2.0 instance resides.
	Instance ID	Select the instance ID of the destination PolarDB-X 2.0 instance.
	Database Account	Enter the account for the destination PolarDB-X 2.0 instance. For the required permissions, see Required database account permissions.
	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. In the CIDR Blocks of DTS Servers dialog box that appears, click Test Connectivity.

Note
Ensure that the IP address segments of the DTS service 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 of Conflicting 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.
Capitalization of Object Names in Destination Instance	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 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 need to set conditions to filter data, right-click the table to be migrated in the Selected Objects section and set the filter conditions in the pop-up dialog box. For more information, see Set Filter Conditions. 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. If you use object name mapping, 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. No selection is 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 contact. 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 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.