Migrate a self-managed SQL Server database to RDS for SQL Server - Data Transmission Service

Prerequisites

For supported versions of self-managed SQL Server databases, see Migration solutions.
You have created a destination RDS for SQL Server instance. For more information, see Create an ApsaraDB RDS for SQL Server instance.
The storage space of the RDS for SQL Server instance must exceed the storage space used by the self-managed SQL Server database.

If your source database meets any of the following conditions, use the RDS for SQL Server backup feature to migrate data. For more information, see Migrate data from a self-managed database to an ApsaraDB RDS instance.

The source instance contains more than 10 databases.
A single database of the source instance backs up its logs more than once per hour.
A single database of the source instance executes more than 100 DDL statements per hour.
Logs are written at a rate of more than 20 MB/s for a single database of the source instance.
The change data capture (CDC) feature needs to be enabled for more than 1,000 tables.

The logs of a database in the source instance contain heap tables, tables without primary keys, compressed tables, or tables with computed columns. You can run the following SQL statements to check whether the source database contains these types of tables:

Check for heap tables in the source database:

SELECT s.name AS schema_name, t.name AS table_name FROM sys.schemas s INNER JOIN sys.tables t ON s.schema_id = t.schema_id AND t.type = 'U' AND s.name NOT IN ('cdc', 'sys') AND t.name NOT IN ('systranschemas') AND t.object_id IN (SELECT object_id FROM sys.indexes WHERE index_id = 0);

Check for tables without primary keys:

SELECT s.name AS schema_name, t.name AS table_name FROM sys.schemas s INNER JOIN sys.tables t ON s.schema_id = t.schema_id AND t.type = 'U' AND s.name NOT IN ('cdc', 'sys') AND t.name NOT IN ('systranschemas') AND t.object_id NOT IN (SELECT parent_object_id FROM sys.objects WHERE type = 'PK');

Check for primary key columns that are not included in clustered index columns in the source database:

SELECT s.name schema_name, t.name table_name FROM sys.schemas s INNER JOIN sys.tables t ON s.schema_id = t.schema_id WHERE t.type = 'U' AND s.name NOT IN('cdc', 'sys') AND t.name NOT IN('systranschemas') AND t.object_id IN ( SELECT pk_colums_counter.object_id AS object_id FROM (select pk_colums.object_id, sum(pk_colums.column_id) column_id_counter from (select sic.object_id object_id, sic.column_id FROM sys.index_columns sic, sys.indexes sis WHERE sic.object_id = sis.object_id AND sic.index_id = sis.index_id AND sis.is_primary_key = 'true') pk_colums group by object_id) pk_colums_counter inner JOIN ( select cluster_colums.object_id, sum(cluster_colums.column_id) column_id_counter from (SELECT sic.object_id object_id, sic.column_id FROM sys.index_columns sic, sys.indexes sis WHERE sic.object_id = sis.object_id AND sic.index_id = sis.index_id AND sis.index_id = 1) cluster_colums group by object_id ) cluster_colums_counter ON pk_colums_counter.object_id = cluster_colums_counter.object_id and pk_colums_counter.column_id_counter != cluster_colums_counter.column_id_counter);

Check for compressed tables in the source database:

SELECT s.name AS schema_name, t.name AS table_name FROM sys.objects t, sys.schemas s, sys.partitions p WHERE s.schema_id = t.schema_id AND t.type = 'U' AND s.name NOT IN ('cdc', 'sys') AND t.name NOT IN ('systranschemas') AND t.object_id = p.object_id AND p.data_compression != 0;

Check for tables that contain computed columns:

SELECT s.name AS schema_name, t.name AS table_name FROM sys.schemas s INNER JOIN sys.tables t ON s.schema_id = t.schema_id AND t.type = 'U' AND s.name NOT IN ('cdc', 'sys') AND t.name NOT IN ('systranschemas') AND t.object_id IN (SELECT object_id FROM sys.columns WHERE is_computed = 1);

Check for tables that contain sparse columns:

SELECT s.name AS schema_name, t.name AS table_name FROM sys.schemas s INNER JOIN sys.tables t ON s.schema_id = t.schema_id AND t.type = 'U' AND s.name NOT IN ('cdc', 'sys') AND t.name NOT IN ('systranschemas') AND t.object_id IN (SELECT object_id FROM sys.columns WHERE is_sparse = 1);

Notes

Note

DTS does not migrate foreign keys from the source database to the destination database. Therefore, cascade and delete operations in the source database are not migrated to the destination database.

Type	Description
Source database limits	Bandwidth requirements: The server that hosts the source database must have sufficient outbound bandwidth. Otherwise, the data migration speed is affected. The tables to be migrated must have primary keys or UNIQUE constraints, and the fields must be unique. Otherwise, duplicate data may appear in the destination database. If you migrate table-level objects and need to edit them, such as by mapping table and column names, a single data migration task supports a maximum of 1,000 tables. If you exceed this limit, an error is reported after you submit the task. In this case, split the tables into multiple migration tasks or configure a task to migrate the entire database. A single data migration task supports a maximum of 10 databases. If you exceed this limit, stability and performance issues may occur. In this case, split the databases into multiple migration tasks. If you configure a task to migrate specific objects instead of an entire database, you cannot migrate tables that have the same name but different schema names to the same destination database. For incremental migration, data logs must meet the following requirements: Logs must be enabled. The backup mode must be set to Full. A full physical backup must have been successfully performed. For an incremental migration task, Data Transmission Service (DTS) requires that the data logs of the source database are retained for more than 24 hours. For a task that includes both full migration and incremental migration, DTS requires that the data logs of the source database are retained for at least 7 days. You can change the log retention period to more than 24 hours after the full migration is complete. Otherwise, the DTS task may fail because DTS cannot obtain the data logs. In extreme cases, data inconsistency or data loss may occur. Issues caused by a log retention period that is shorter than the required period are not covered by the DTS Service-Level Agreement (SLA). To enable change data capture (CDC) for the tables to be migrated from the source database, the following conditions must be met. Otherwise, the precheck fails. The value of the `srvname` field in the `sys.sysservers` view must be the same as the return value of the `SERVERPROPERTY` function. If the source database is a self-managed SQL Server instance, the database owner must be `sa`. If the source database is an RDS for SQL Server instance, the database owner must be `sqlsa`. If the source database is Enterprise Edition, it must be SQL Server 2008 or later. If the source database is Standard Edition, it must be SQL Server 2016 SP1 or later. If the source database is SQL Server 2017 (Standard or Enterprise Edition), upgrade the database version. DTS uses the fn_log function to obtain source database logs. This function has performance bottlenecks. Do not clear the source database logs too early. Otherwise, the DTS task may fail. Source database operation limits: During initial schema synchronization and full data migration, do not perform DDL operations to change the schemas of databases or tables. Otherwise, the data migration 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 ensure real-time data consistency, select Initial Schema Synchronization, Full Data Migration, and Incremental Data Migration. If the source database is a read-only instance, DDL operations cannot be migrated. If the source database is an Azure SQL Database, a DTS instance can migrate only one database. If the source database is an RDS for SQL Server instance and the migration task includes incremental migration, disable transparent data encryption (TDE) to ensure the stability of the DTS instance. For more information, see Disable TDE. If you use the `sp_rename` command to rename objects such as stored procedures in the source database before the initial schema synchronization task runs, the task may not work as expected or may fail. Note Use the `ALTER` command to rename objects in the database. In hybrid log parsing mode, you cannot consecutively perform multiple operations to add or remove columns in the source database within an interval of less than 10 minutes. For example, if you run the following SQL statements consecutively, the task reports an error. `ALTER TABLE test_table DROP COLUMN Flag; ALTER TABLE test_table ADD Remark nvarchar(50) not null default('');` If the source database is a Web Edition RDS for SQL Server instance, you must set SQL Server Incremental Synchronization Mode to Incremental Synchronization Based on Logs of Source Database (Heap tables are not supported) when you configure the task. During full data migration, make sure that the `READ_COMMITTED_SNAPSHOT` transaction processing mode parameter is enabled for the source database. This prevents shared locks from affecting data writes. Otherwise, exceptions such as data inconsistency and instance failures may occur. Exceptions caused by this issue are not covered by the DTS SLA.
Other limits	Data of the CURSOR, ROWVERSION, SQL_VARIANT, HIERARCHYID, POLYGON, GEOMETRY, and GEOGRAPHY data types cannot be migrated. If data cannot be written to a field of the TIMESTAMP data type in the destination database, DTS does not support full and incremental migration. This may cause data inconsistency or task failures. To migrate triggers from the source database, the database account used for the task must have Owner permissions on the destination database. If you select Incremental Synchronization Based on Logs of Source Database (Heap tables are not supported) for SQL Server Incremental Synchronization Mode in the Configure Objects stage, the tables to be migrated must have a clustered index that contains primary key columns. The tables to be migrated cannot be heap tables, tables without primary keys, compressed tables, tables with computed columns, or tables with sparse columns. In mixed log parsing mode, these restrictions do not apply. Note For more information about how to view information about these tables, see How to view information about heap tables, tables without primary keys, compressed tables, tables with computed columns, and tables with sparse columns in SQL Server. If you set SQL Server Incremental Synchronization Mode to Log-based Parsing for Non-heap Tables and CDC-based Incremental Synchronization for Heap Tables (Hybrid Log-based Parsing) in the Configure Objects step, the following limits also apply: Incremental migration by DTS depends on the CDC component. Make sure that the CDC job in the source database is running. Otherwise, the DTS task fails. By default, the incremental data stored in the CDC component is retained for 3 days. We recommend that you use the `exec console.sys.sp_cdc_change_job @job_type = 'cleanup', @retention= <time>;` command to adjust the retention period. Note `<time>` specifies the time in minutes. If the number of incremental change SQL statements for a single table in the source database exceeds 10 million per day, we recommend that you set `<time>` to 1440. In a single migration task, we recommend that you enable CDC for no more than 1,000 tables. Otherwise, task latency or instability may occur. The prerequisite module of an incremental migration task enables CDC for the source database. During this process, the source database may be briefly locked due to the limits of the SQL Server database kernel. If you set SQL Server Incremental Synchronization Mode to Polling and querying CDC instances for incremental synchronization in the Configure Objects step, the following limits also apply: The source database account used by the DTS instance must have the permissions to enable CDC. To enable database-level CDC, you need an account with the sysadmin role. To enable table-level CDC, you need a privileged account. Note The privileged account (server administrator) provided by the Azure SQL Database console meets the requirements. For vCore-based databases, all instance types support CDC. For DTU-based databases, only instance types of S3 and later support CDC. The privileged account of Amazon RDS for SQL Server meets the requirements and can be used to enable database-level CDC for stored procedures. Clustered columnstore index tables do not support CDC. The prerequisite module of an incremental migration task enables CDC for the source database. During this process, the source database may be briefly locked due to the limits of the SQL Server database kernel. DTS polls the CDC instance of each table in the source database to obtain incremental data. Therefore, we recommend that you migrate no more than 1,000 tables from the source database. Otherwise, task latency or instability may occur. By default, the incremental data stored in the CDC component is retained for 3 days. We recommend that you use the `exec console.sys.sp_cdc_change_job @job_type = 'cleanup', @retention= <time>;` command to adjust the retention period. Note `<time>` specifies the time in minutes. If the number of incremental change SQL statements for a single table in the source database exceeds 10 million per day, we recommend that you set `<time>` to 1440. You cannot consecutively perform operations to add or remove columns. For example, you cannot perform more than two DDL operations to add or remove columns within one minute. Otherwise, the task may fail. You cannot change the CDC instance of the source database. Otherwise, the task may fail or data may be lost. If you migrate data across different versions, check the compatibility in advance. To ensure the accuracy of incremental data migration latency, DTS creates the dts_cdc_sync_ddl trigger, the dts_sync_progress heartbeat table, and the dts_cdc_ddl_history DDL storage table in the source database in log parsing mode. In hybrid incremental synchronization mode, DTS creates the dts_cdc_sync_ddl trigger, the dts_sync_progress heartbeat table, and the dts_cdc_ddl_history DDL storage table, and enables database-level CDC and CDC for some tables. We recommend that the data change rate of tables with CDC enabled in the source database does not exceed 1,000 records per second (RPS). Before you migrate data, evaluate the performance of the source and destination databases. We recommend that you migrate data during off-peak hours. Otherwise, DTS consumes read and write resources on the source and destination databases during full data migration, which may increase the database load. Full data migration involves concurrent INSERT operations, which cause table fragmentation in the destination database. Therefore, after full data migration is complete, the table storage space in the destination database is larger than that in the source instance. Confirm whether the migration precision that DTS provides for columns of the FLOAT or DOUBLE data type meets your business requirements. DTS reads the values of these columns using `ROUND(COLUMN,PRECISION)`. If you do not specify the precision, DTS migrates FLOAT values with a precision of 38 and DOUBLE values with a precision of 308. DTS attempts to resume a failed migration task within 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 account that DTS uses to access the destination instance. This prevents the source data from overwriting the data in the destination instance after the task is automatically resumed. If a migration task includes incremental data migration, you cannot reindex. Otherwise, the task may fail or data may be lost. Note You cannot change the primary keys of tables for which CDC is enabled. If the number of tables for which CDC is enabled in a single migration task is greater than the value of The maximum number of tables for which CDC is enabled that DTS supports., the precheck fails. If a task includes incremental migration and the data to be written to a single field of a table with CDC enabled exceeds 64 KB, you must run the `exec sp_configure 'max text repl size', -1;` command to adjust the configuration of the source database in advance. Note By default, a CDC job can process a single field with a maximum length of 64 KB. For incremental migration, disable the triggers and foreign keys that are enabled in the destination database. Otherwise, the migration task fails. If multiple DTS instances use the same SQL Server database as the source, their incremental data ingestion modules are independent of each other. If the task fails, DTS technical support will attempt to recover it within 8 hours. During the recovery process, operations such as restarting the task or adjusting its parameters may be performed. Note When parameters are adjusted, only DTS task parameters are modified. Database parameters remain unchanged.The parameters that may be modified include but are not limited to those described in Modify instance parameters. SQL Server is a commercial closed-source database. Due to known or unknown format-specific limits, issues may occur when DTS performs CDC and parsing on SQL Server logs. Therefore, before you enable incremental synchronization or migration for a SQL Server source in a production environment, we recommend that you perform a comprehensive proof of concept (POC) test. The test must cover all business change types, table schema changes, and business peak-hour stress tests. Due to the unpredictable nature of the SQL Server log format, you must ensure that the business logic in the production environment is consistent with that in the POC test. This is key to ensuring the high efficiency and stability of DTS.
Special cases	If the source instance is an RDS for SQL Server instance, DTS creates an `rdsdt_dtsacct` account in the source instance for data migration. Do not delete this account or change its password while the task is running. Otherwise, the task may fail. For more information, see System accounts. If the destination instance is an RDS for SQL Server instance, DTS automatically creates a database in the instance. If the name of the database to be migrated does not comply with the naming conventions of RDS for SQL Server, you must create a database in the destination instance before you configure the migration task. For more information, see Create a database.

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.
- Objects that support schema migration include tables, views, table triggers, synonyms, SQL stored procedures, SQL functions, plan guides, user-defined types, rules, defaults, and sequences.
- Objects that do not support schema migration include assemblies, service brokers, full-text indexes, full-text catalogs, distributed schemas, distributed functions, CLR stored procedures, CLR scalar functions, CLR table-valued functions, internal tables, system objects, and aggregate functions.
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 that support incremental migration

Operation type	SQL operation
DML	INSERT, UPDATE, DELETE Note UPDATE statements that only update large objects are not supported for incremental migration.
DDL	CREATE TABLE ALTER TABLE Only includes ADD COLUMN and DROP COLUMN DROP TABLE CREATE INDEX, DROP INDEX Note Transactional DDL operations are not supported. For example, a DDL operation that adds multiple columns in a single SQL statement or a single SQL statement that contains both DDL and DML operations may cause data loss. DDL operations that contain user-defined types are not supported. Online DDL operations are not supported. DDL operations that use reserved keywords as property names are not supported. DDL operations executed by system stored procedures are not supported. TRUNCATE TABLE operations are not supported. Partitions and table definitions that contain functions are not supported.

Permissions required for database accounts

Database	Schema migration	Full migration	Incremental migration
Self-managed SQL Server database	SELECT permission	SELECT permission	sysadmin
RDS for SQL Server instance	Read and write permissions

To create a database account and grant permissions:

For a self-managed SQL Server database, see CREATE USER.
For an RDS for SQL Server instance, see Create a standard account, a privileged account, or a global read-only account and Modify the permissions of an account.

Data migration process

To resolve object dependencies and improve migration success rates, DTS migrates SQL Server schema and data in the following order:

Perform schema migration for tables, views, synonyms, user-defined types, rules, defaults, and plan guides.
Perform full data migration.
Perform schema migration for SQL stored procedures, SQL functions, triggers, and foreign keys.
Perform incremental data migration.

Preparations

Note

To perform incremental migration, configure transaction log settings and create a clustered index on the self-managed SQL Server database before you configure the data migration task.

Important

To migrate multiple databases, repeat steps 1 to 3 in this section. Otherwise, data inconsistency may occur.

In the self-managed SQL Server database, run the following command to set the recovery model of the database to be migrated to full recovery mode:
```
use master;
GO
ALTER DATABASE <database_name> SET RECOVERY FULL WITH ROLLBACK IMMEDIATE;
GO
```
Parameters:

<database_name>: The name of the database to be migrated.

Example:
```
use master;
GO
ALTER DATABASE mytestdata SET RECOVERY FULL WITH ROLLBACK IMMEDIATE;
GO
```
Run the following command to perform a logical backup of the database to be migrated. Skip this step if a logical backup has already been performed.
```
BACKUP DATABASE <database_name> TO DISK='<physical_backup_device_name>';
GO
```
Parameters:
- <database_name>: The name of the database to be migrated.
- <physical_backup_device_name>: The path and file name of the backup file.
Example:
```
BACKUP DATABASE mytestdata TO DISK='D:\backup\dbdata.bak';
GO
```
Run the following command to back up the transaction log of the database to be migrated.
```
BACKUP LOG <database_name> to DISK='<physical_backup_device_name>' WITH init;
GO
```
Parameters:
- <database_name>: The name of the database to be migrated.
- <physical_backup_device_name>: The path and file name of the backup file.
Example:
```
BACKUP LOG mytestdata TO DISK='D:\backup\dblog.bak' WITH init;
GO
```

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	Configuration	Description
None	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 Information	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 SQL Server.
	Connection Type	Select Public IP. Note When you select a self-managed database, you also need to perform the corresponding preparations. For more information, see Preparations overview.
	Instance Region	Select the region where the self-managed SQL Server database resides.
	Hostname or IP Address	Enter the endpoint of the self-managed SQL Server database. In this example, enter the public endpoint.
	Port	Enter the service port of the self-managed SQL Server database. The default port is 1433.
	Database Account	Enter the database account of the self-managed SQL Server database. For information about the required permissions, see Permissions required for database accounts.
	Database Password	Enter the password for the database account.
	Encryption	Specifies whether to encrypt the connection to the source database. Select Non-encrypted or SSL-encrypted based on your business requirements. If SSL encryption is disabled for the source database, select Non-encrypted. If SSL encryption is enabled for the source database, select SSL-encrypted. By default, DTS trusts the server certificate.
Destination Database Information	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 SQL Server.
	Connection Type	Select Cloud Instance.
	Instance Region	Select the region where the destination RDS for SQL Server instance resides.
	Instance ID	Select the ID of the destination RDS for SQL Server instance.
	Database Account	Enter the database account of the destination RDS for SQL Server instance. For information about the required permissions, see Permissions required for database accounts.
	Database Password	Enter the password for the database account.
	Encryption	Specifies whether to encrypt the connection to the destination database. Select Non-encrypted or SSL-encrypted based on your business requirements. If SSL encryption is disabled for the destination database, select Non-encrypted. If SSL encryption is enabled for the destination database, select SSL-encrypted. By default, DTS trusts the server certificate.

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.

Configuration	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.
Method to Migrate Triggers in Source Database	Select a trigger migration method as needed. If no triggers are involved, skip this setting. For more information, see Configure how to synchronize or migrate triggers. Note This option is available only when Migration Types includes both Schema Migration and Incremental Data Migration.
SQL Server Incremental Synchronization Mode	Log-based Parsing for Non-heap Tables and CDC-based Incremental Synchronization for Heap Tables (Hybrid Log-based Parsing): Advantages: Supports scenarios that involve source heap tables, tables without primary keys, compressed tables, or tables with computed columns. Provides high link stability. This mode can obtain complete DDL statements and supports a wide range of DDL scenarios. Disadvantages: DTS creates the `dts_cdc_sync_ddl` trigger, the `dts_sync_progress` heartbeat table, and the `dts_cdc_ddl_history` DDL storage table in the source database. It also enables database-level CDC and CDC for some tables. You cannot execute `SELECT INTO`, `TRUNCATE`, or `RENAME COLUMN` statements on tables with CDC enabled in the source database. You cannot manually delete triggers created by DTS in the source database. Incremental Synchronization Based on Logs of Source Database (Heap tables are not supported): Advantage: This mode is non-intrusive to the source database. Disadvantage: This mode does not support scenarios that involve source heap tables, tables without primary keys, compressed tables, or tables with computed columns. Polling and querying CDC instances for incremental synchronization: Advantages: Supports full and incremental migration when the source database is Amazon RDS for SQL Server, Azure SQL Database, Azure SQL Managed Instance, Azure SQL Server on Virtual Machine, or Google Cloud SQL for SQL Server. This mode uses the native CDC component of SQL Server to obtain incremental data, which improves the stability of incremental migration and reduces network bandwidth usage. Disadvantages: The source database account used by the DTS instance must have the permissions to enable CDC. Incremental data migration has a latency of about 10 seconds. When you migrate multiple tables across multiple databases, you may encounter stability and performance issues. Note This setting appears only when Migration Types includes Incremental Data Migration.
The maximum number of tables for which CDC is enabled that DTS supports.	We recommend that you, based on your business requirements, set the maximum number of tables for which CDC is enabled that a DTS task supports. Default value: 1,000. Note This parameter is unavailable if you set the SQL Server Incremental Synchronization Mode parameter to Incremental Synchronization Based on Logs of Source Database (Heap tables are not supported).
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.
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 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 Individual table column mapping. 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 Using the object name mapping feature may cause dependent objects to fail migration. To filter data using a WHERE clause, right-click the table to migrate in the Selected Objects box and set the filter condition in the dialog box. For instructions, see Configure filter conditions. To select SQL operations to migrate at the database or table level, right-click the migration object in the Selected Objects box and select the desired operations in the dialog box.

Click Next: Advanced Settings to configure advanced parameters.

Configuration	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	As needed, you can select an environment tag to identify the instance. No selection is needed for this example.
Configure ETL	Choose whether to enable the extract, transform, and load (ETL) feature. For more information, see What is ETL? Valid values: Yes: Enables the ETL feature. Enter data processing statements in the code editor. For more information, see Configure ETL in a data migration or data synchronization task. No: Disables 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.

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.