Migrate data from an ApsaraDB RDS for SQL Server instance to a DataHub project - Data Transmission Service

This topic describes how to migrate data from an ApsaraDB RDS for SQL Server instance to a DataHub project by using Data Transmission Service (DTS).

Prerequisites

The version of the source ApsaraDB RDS for SQL Server instance is supported by DTS. For more information about the SQL Server versions that are supported by the source ApsaraDB RDS for SQL Server instance, see Overview of data migration scenarios.
DataHub is activated, and a project is created to receive the data to be migrated. For more information, see Get started with DataHub and Manage projects.
Multiple DTS instances are purchased to configure multiple data migration tasks if the source ApsaraDB RDS for SQL Server instance meets one of the following conditions:
- The source instance contains more than 10 databases.
- A single database of the source instance backs up its logs at an interval of less than 1 hour.
- A single database of the source instance executes more than 100 DDL statements each hour.
- Logs are written at a rate of 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 in the source ApsaraDB RDS for SQL Server instance.

Limits

Note

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

Category	Description
Limits on the source database	The server on which the source database is deployed must have sufficient outbound bandwidth. Otherwise, the data migration speed decreases. The tables to be migrated must have PRIMARY KEY or UNIQUE constraints and all fields must be unique. Otherwise, the destination database may contain duplicate data records. If you select tables as the objects to be migrated and you need to edit the tables in the destination database, such as renaming tables or columns, you can migrate up to 1,000 tables in a single data migration task. If you run a task to migrate more than 1,000 tables, a request error occurs. In this case, we recommend that you configure multiple tasks to migrate the tables or configure a task to migrate the entire database. You can run a single data migration task to migrate up to 10 databases. If you want to migrate more than 10 databases, we recommend that you configure multiple tasks to migrate the databases. Otherwise, the performance and stability of your data migration task may be compromised. If you want to migrate incremental data, make sure that the following requirements are met: The data logging feature must be enabled. The backup mode must be set to Full and full physical backup must be performed. If you perform only incremental data migration, the data logs of the source database must be retained for more than 24 hours. If you perform both full data migration and incremental data migration, the data logs of the source database must be retained for at least seven days. Otherwise, Data Transmission Service (DTS) may fail to obtain the data logs and the task may fail. In some cases, data inconsistency or loss may even occur. After full data migration is complete, you can set the retention period to more than 24 hours. Make sure that you set the retention period of data logs based on the preceding requirements. Otherwise, the Service Level Agreement (SLA) of DTS does not guarantee service reliability or performance. If the change data capture (CDC) feature needs to be enabled for the tables that you want to migrate 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 is the same as the return value of the SERVERPROPERTY function. If the source database is a self-managed SQL Server database, the database owner must be the sa user. If the source database is an ApsaraDB RDS for SQL Server database, the database owner must be the sqlsa user. If the source database is of the Enterprise edition, you must use SQL Server 2008 or later. If the source database is of the Standard edition, you must use SQL Server 2016 SP1 or later. If the source database is of the Standard or Enterprise edition and its version is SQL Server 2017, we recommend that you update the version. DTS uses the fn_log function to obtain the logs of the source database. However, this function has performance bottlenecks. We recommend that you do not clear the logs of the source database before the task is complete. Otherwise, the task may fail. Limits on operations on the source database: During schema migration and full data migration, do not execute DDL statements to change the schemas of databases or tables. Otherwise, the data migration task fails. If you perform only full data migration, do not write data to the source database during data migration. Otherwise, data will be inconsistent between the source and destination databases. To ensure data consistency, we recommend that you select Schema Migration, Full Data Migration, and Incremental Data Migration as the migration types. In hybrid log-based parsing mode, you cannot perform multiple operations to add columns to or remove columns from the source database within 10 minutes. For example, if you execute the following SQL statements within 10 minutes, an error is reported for the task. `ALTER TABLE test_table DROP COLUMN Flag; ALTER TABLE test_table ADD Remark nvarchar(50) not null default('');`
Other limits	Only incremental data migration and schema migration are supported. Full data migration is not supported. A single string in the destination DataHub project cannot exceed 2 MB in length. Limits on the objects to be migrated: DTS supports initial schema migration for the following types of objects: schema, table, view, function, and procedure. DTS does not migrate the schemas of the following objects: assemblies, service brokers, full-text indexes, full-text catalogs, distributed schemas, distributed functions, common language runtime (CLR) stored procedures, CLR scalar-valued functions, CLR table-valued functions, internal tables, systems, or aggregate functions. DTS does not migrate data of the following types: CURSOR, ROWVERSION, SQL_VARIANT, HIERARCHYID, POLYGON, GEOMETRY, and GEOGRAPHY. DTS does not migrate tables that contain computed columns. Before you migrate data, evaluate the impact of data migration on the performance of the source and destination databases. We recommend that you migrate data during off-peak hours. During full data migration, DTS uses the read and write resources of the source database and destination cluster. This may increase the loads on the database servers. In Incremental Synchronization Based on Logs of Source Database mode, DTS creates a trigger named dts_cdc_sync_ddl, a heartbeat table named dts_sync_progress, and a DDL history table named dts_cdc_ddl_history in the source database to ensure that the latency of data migration is accurate. In hybrid log-based parsing incremental synchronization mode, DTS creates a trigger named dts_cdc_sync_ddl, a heartbeat table named dts_sync_progress, and a DDL history table named dts_cdc_ddl_history and enables CDC for the source database and specific tables. We recommend that you set the maximum number of records per second to 1,000 for the tables for which CDC is enabled in the source database. During full data migration, concurrent INSERT operations cause fragmentation in the tables of the destination database. After full data migration is complete, the size of used tablespace of the destination database is larger than that of the source database. If you use tools other than DTS to write data to the destination database, data inconsistency between the source and destination databases may occur.
Special cases	If the source instance is an ApsaraDB RDS for SQL Server instance, DTS automatically creates an account named `rdsdt_dtsacct` on the ApsaraDB RDS for SQL Server instance. This account is used for data migration. Do not delete this account or change the password of this account when your data migration task is running. Otherwise, the task may fail. For more information, see System accounts.

Billing

Migration type	Task configuration fee	Data transfer fee
Schema migration	Free of charge.	Free of charge in this example. Note Charged only when data is migrated from Alibaba Cloud over the Internet. For more information, see Billing overview.
Incremental data migration	Charged. For more information, see Billing overview.

SQL operations that can be incrementally migrated

Operation type	SQL statement
DML	INSERT, UPDATE, and DELETE

Permissions required for database accounts

Instance	Schema migration	Incremental data migration	References
Source ApsaraDB RDS for SQL Server instance	The read permissions on the objects to migrate	The owner permission on the objects to be migrated	Create a privileged account or a standard account and Modify the permissions of an account

Procedure

Go to the Data Migration Tasks page.
1. Log on to the Data Management (DMS) console.
2. In the top navigation bar, move the pointer over DTS.
3. Choose DTS (DTS) > Data Migration.
Note
- The actual operations may vary based on the mode and layout of the DMS console. For more information, see Simple mode and Customize the layout and style of the DMS console.
- You can also go to the Data Migration page of the new DTS console.
From the drop-down list on the right side of Data Migration Tasks, select the region in which your data migration instance resides.
Note
If you use the new DTS console, you must select the region in which the data migration instance resides in the upper-left corner.

Click Create Task. On the Create Task page, configure the source and destination databases. The following table describes the parameters.

Warning

After you configure the source and destination databases, we recommend that you read the Limits that are displayed in the upper part of the page. Otherwise, the task may fail or data inconsistency may occur.

Section	Parameter	Description
N/A	Task Name	The name of the task. DTS automatically generates a task name. We recommend that you specify an informative name to identify the task. You do not need to specify a unique task name.
Source Database	Select an existing DMS database instance. (Optional. If you have not registered a DMS database instance, ignore this option and configure database settings in the section below.)	The database instance that you want to use. You can choose whether to use an existing instance based on your business requirements. If you select an existing instance, DTS automatically populates the parameters for the database. If you do not select an existing instance, you must manually configure parameters for the database.
	Database Type	The type of the source database. Select SQL Server.
	Access Method	The access method of the source database. Select Alibaba Cloud Instance.
	Instance Region	The region in which the source ApsaraDB RDS for SQL Server instance resides.
	Replicate Data Across Alibaba Cloud Accounts	Specifies whether to migrate data across Alibaba Cloud accounts. In this example, No is selected.
	RDS Instance ID	The ID of the source ApsaraDB RDS for SQL Server instance.
	Database Account	The database account of the source ApsaraDB RDS for SQL Server instance. For more information about the permissions that are required for the account, see the Permissions required for database accounts section of this topic.
	Database Password	The password that is used to access the database instance.
Destination Database	Select an existing DMS database instance. (Optional. If you have not registered a DMS database instance, ignore this option and configure database settings in the section below.)	The database instance that you want to use. You can choose whether to use an existing instance based on your business requirements. If you select an existing instance, DTS automatically populates the parameters for the database. If you do not select an existing instance, you must manually configure parameters for the database.
	Database Type	The type of the destination database. Select DataHub.
	Access Method	The access method of the destination database. Select Alibaba Cloud Instance.
	Instance Region	The region in which the destination DataHub project resides.
	Project	The name of the destination DataHub project.Project

In the lower part of the page, click Test Connectivity and Proceed.
If the source or destination database is an Alibaba Cloud database instance, such as an ApsaraDB RDS for MySQL or ApsaraDB for MongoDB instance, DTS automatically adds the CIDR blocks of DTS servers to the IP address whitelist of the instance. If the source or destination database is a self-managed database hosted on an Elastic Compute Service (ECS) instance, DTS automatically adds the CIDR blocks of DTS servers to the security group rules of the ECS instance, and you must make sure that the ECS instance can access the database. If the self-managed database is hosted on multiple ECS instances, you must manually add the CIDR blocks of DTS servers to the security group rules of each ECS instance. If the source or destination database is a self-managed database that is deployed in a data center or provided by a third-party cloud service provider, you must manually add the CIDR blocks of DTS servers to the IP address whitelist of the database to allow DTS to access the database. For more information, see the CIDR blocks of DTS servers section of the Add the CIDR blocks of DTS servers topic.
Warning
If the public CIDR blocks of DTS servers are automatically or manually added to the whitelist of a database instance or to the security group rules of an ECS instance, security risks may arise. Therefore, before you use DTS to migrate data, you must understand and acknowledge the potential risks and take preventive measures, including but not limited to the following measures: enhancing the security of your username and password, limiting the ports that are exposed, authenticating API calls, regularly checking the whitelist or security group rules and forbidding unauthorized CIDR blocks, or connecting the database instance to DTS by using Express Connect, VPN Gateway, or Smart Access Gateway.

Configure the objects to be migrated and advanced settings. The following table describes the parameters.

Parameter	Description
Migration Types	You can select only Schema Migration and Incremental Data Migration. Full Data Migration cannot be selected. Note If Incremental Data Migration is not selected, we recommend that you do not write data to the source database during data migration. This ensures data consistency between the source and destination databases.
Naming Rules of Additional Columns	When DTS migrates data to DataHub projects, DTS adds additional columns to the destination topic. If the names of additional columns are the same as the names of existing columns in the destination topic, data migration fails. You can select New Rule or Previous Rule for this parameter based on your business requirements. Warning Before you configure this parameter, check whether additional columns have name conflicts with existing columns in the destination topic. If conflicts exist, the data migration task may fail or data may be lost. For more information, see Modify the naming rules for additional columns.
Processing Mode of Conflicting Tables	Precheck and Report Errors: checks whether the destination database contains tables that use the same names as tables in the source database. If the source and destination databases do not contain tables that have identical table names, the precheck is passed. Otherwise, an error is returned during the precheck and the data migration task cannot be started. Note If the source and destination databases contain tables with identical names and the tables in the destination database cannot be deleted or renamed, you can use the object name mapping feature to rename the tables that are migrated to the destination database. For more information, see Map object names. Ignore Errors and Proceed: skips the precheck for identical table names in the source and destination databases. Warning If you select Ignore Errors and Proceed, data inconsistency may occur and your business may be exposed to the following potential risks: If the source and destination databases have the same schema, and a data record has the same primary key as an existing data record in the destination database, the following scenarios may occur: During full data migration, DTS does not migrate the data record to the destination database. The existing data record in the destination database is retained. During incremental data migration, DTS migrates the data record to the destination database. The existing data record in the destination database is overwritten. If the source and destination databases have different schemas, only specific columns are migrated or the data migration task fails. Proceed with caution.
Capitalization of Object Names in Destination Instance	The capitalization of database names, table names, and column names in the destination instance. By default, DTS default policy is selected. You can select other options to make sure that the capitalization of object names is consistent with that of the source or destination database. For more information, see Specify the capitalization of object names in the destination instance.
Source Objects	Select one or more objects from the Source Objects section. Click the icon to add the objects to the Selected Objects section. Note You can select columns, tables, or databases as the objects to be migrated.
Selected Objects	To rename an object that you want to migrate to the destination instance, right-click the object in the Selected Objects section. For more information, see Map the name of a single object. To rename multiple objects at a time, click Batch Edit in the upper-right corner of the Selected Objects section. For more information, see Map multiple object names at a time. Note The database name cannot be mapped. If you use the object name mapping feature to rename a database, other objects that are dependent on the database may fail to be migrated. To specify WHERE conditions to filter data, right-click an object in the Selected Objects section. In the dialog box that appears, specify the conditions. For more information, see Specify filter conditions. To incrementally migrate SQL operations performed on a specific database or table, right-click the object in the Selected Objects section. In the dialog box that appears, select the SQL operations that you want to incrementally migrate. For more information, see the SQL operations that can be incrementally migrated section of this topic.

Click Next: Advanced Settings to configure advanced settings.

Parameter or setting	Description
Dedicated Cluster for Task Scheduling	By default, DTS schedules the task to a shared cluster. You do not need to configure this parameter. You can purchase a dedicated cluster of the specified specifications to run data migration tasks. For more information, see What is a DTS dedicated cluster?
Set Alerts	Specifies whether to configure alerting for the data migration task. If the task fails or the migration latency exceeds the specified threshold, the alert contacts receive notifications. Valid values: No: does not configure alerting. Yes: configures alerting. In this case, you must also configure the alert threshold and alert notification settings. For more information, see Configure monitoring and alerting when you create a DTS task.
Retry Time for Failed Connections	The retry time range for failed connections. If the source or destination database fails to be connected after the data migration task is started, DTS immediately retries a connection within the retry time range. Valid values: 10 to 1440. Unit: minutes. Default value: 720. We recommend that you set the parameter to a value greater than 30. If DTS is reconnected to the source and destination databases within the specified retry time range, DTS resumes the data migration task. Otherwise, the data migration task fails. Note If you specify different retry time ranges for multiple data migration tasks that share the same source or destination database, the value that is specified later takes precedence. When DTS retries a connection, you are charged for the DTS instance. We recommend that you specify the retry time range based on your business requirements. You can also release the DTS instance at the earliest opportunity after the source database and destination instance are released.
Retry Time for Other Issues	The retry time range for other issues. For example, if DDL or DML operations fail to be performed after the data migration task is started, DTS immediately retries the operations within the retry time range. Valid values: 1 to 1440. Unit: minutes. Default value: 10. We recommend that you set the parameter to a value greater than 10. If the failed operations are successfully performed within the specified retry time range, DTS resumes the data migration task. Otherwise, the change tracking task fails. Important The value of the Retry Time for Other Issues parameter must be smaller than the value of the Retry Time for Failed Connections parameter.
Enable Throttling for Incremental Data Migration	You can specify whether to enable throttling for the incremental data migration task. If you select Yes, you can configure the RPS of Incremental Data Migration and BPS of Incremental Data Migration parameters based on your business requirements to relieve the load on the destination cluster. Note You can configure this parameter only if you select Incremental Data Migration as a migration type.Migration Types
Environment Tag	The environment tag that is used to identify the DTS instance. You can select an environment tag based on your business requirements. In this example, no environment tag is selected.
Configure ETL	Specifies whether to enable the extract, transform, and load (ETL) feature. For more information, see What is ETL? Valid values: Yes: configures the ETL feature. You can enter data processing statements in the code editor. For more information, see Configure ETL in a data migration or data synchronization task. No: does not configure the ETL feature.

In the lower part of the page, click Next: Save Task Settings and Precheck.
You can move the pointer over Next: Save Task Settings and Precheck and click Preview OpenAPI parameters to view the parameters to be specified when you call the relevant API operation to configure the DTS task.
Note
- Before you can start the data migration task, DTS performs a precheck. You can start the data migration task only after the task passes the precheck.
- If the task fails to pass the precheck, click View Details next to each failed item. After you analyze the causes based on the check results, troubleshoot the issues. Then, run a precheck again.
- If an alert is triggered for an item during the precheck:
  If an alert item cannot be ignored, click View Details next to the failed item and troubleshoot the issues. Then, run a precheck again.
  If the alert item can be ignored, click Confirm Alert Details. In the View Details dialog box, click Ignore. In the message that appears, click OK. Then, click Precheck Again to run a precheck again. If you ignore the alert item, data inconsistency may occur, and your business may be exposed to potential risks.
Wait until Success Rate becomes 100%. Then, click Next: Purchase Instance.

On the Purchase Instance page, configure the Instance Class parameter for the data migration instance. The following table describes the parameters.

Section	Parameter	Description
New Instance Class	Resource Group Settings	The resource group to which the data migration instance belongs. Default value: default resource group. For more information, see What is Resource Management?
New Instance Class	Instance Class	DTS provides instance classes that vary in the migration speed. You can select an instance class based on your business scenario. For more information, see Specifications of data migration instances.

Read and agree to Data Transmission Service (Pay-as-you-go) Service Terms by selecting the check box.
Click Buy and Start. In the dialog box that appears, click OK.
You can view the progress of the task in the task list.