This topic describes how to migrate incremental data from a self-managed SQL Server database to an ApsaraDB RDS for SQL Server instance by using Data Transmission Service (DTS). DTS supports schema migration, full data migration, and incremental data migration. When you migrate data from a self-managed SQL Server database, you can select all of the supported migration types to ensure service continuity.

Note For information about how to perform only full data migration, see Migrate full data from a self-managed SQL Server database to an ApsaraDB RDS for SQL Server instance.

Prerequisites

  • The version of the self-managed SQL Server database is 2008, 2008 R2, 2012, 2014, 2016, or 2017.
    Note
    • If a primary/secondary switchover is performed in an SQL Server cluster or Always On availability group (AOAG), the log serial numbers of the primary database and the secondary database become inconsistent. In this case, DTS considers that the logs of the source database are discontinuous, and the migration task fails. Therefore, you cannot use an SQL Server cluster or an SQL Server AOAG as the source database.
    • If you migrate data between different versions of databases, make sure that the database versions are compatible.
  • The tables to be migrated from the self-managed SQL Server database have primary keys or UNIQUE NOT NULL indexes.
  • The available storage space of the ApsaraDB RDS for SQL Server instance is larger than the total size of the data in the self-managed SQL Server database.

Precautions

  • DTS uses read and write resources of the source and destination databases during full data migration. This may increase the loads of the database servers. If the database performance is unfavorable, the specification is low, or the data volume is large, database services may become unavailable. For example, DTS occupies a large amount of read and write resources in the following cases: a large number of slow SQL queries are performed on the source database, the tables have no primary keys, or a deadlock occurs in the destination database. 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. For example, you can migrate data when the CPU utilization of the source and destination databases is less than 30%.
  • To ensure that the incremental data migration task runs as expected, do not frequently back up the source database. We recommend that you retain log files for more than three days. Otherwise, you cannot retrieve log files after they are truncated.
  • To ensure that the delay time of incremental data migration is accurate, DTS adds a heartbeat table to the self-managed SQL Server database. The name of the heartbeat table is Source table name_dts_mysql_heartbeat.
  • DTS automatically creates a destination database in the ApsaraDB RDS for SQL Server instance. However, if the name of the source database is invalid, you must create a database in the ApsaraDB RDS for SQL Server instance before you configure the data migration task.
    Note For more information about the naming conventions of ApsaraDB RDS for SQL Server databases and how to create a database, see Create a database on an ApsaraDB RDS for SQL Server instance.
  • If a data migration task fails, DTS automatically resumes the task. Before you switch your workloads to the destination instance, stop or release the data migration task. Otherwise, the data in the source database will overwrite the data in the destination instance after the task is resumed.

Limits

  • DTS does not migrate the schemas of assemblies, service brokers, full-text indexes, full-text catalogs, distributed schemas, distributed functions, CLR stored procedures, CLR scalar-valued functions, CLR table-valued functions, internal tables, systems, or aggregate functions.
  • DTS does not migrate data of the SQL_VARIANT type.
  • DTS does not migrate tables that contain computed columns.
  • A single data migration task can migrate incremental data from only one database. To migrate incremental data from multiple databases, you must create a data migration task for each database.

Migration types

  • Schema migration

    DTS migrates the schemas of the required objects to the destination database. DTS supports schema migration for the following types of objects: table, view, trigger, synonym, SQL stored procedure, SQL function, plan guide, user-defined type, rule, default, and sequence.

  • Full data migration

    DTS migrates historical data of the required objects from the self-managed SQL Server database to the destination database.

  • Incremental data migration

    After full data migration is complete, DTS migrates incremental data from the self-managed SQL Server database to the destination database.

SQL operations that can be synchronized during incremental data migration

  • INSERT, UPDATE, and DELETE
    Note If an UPDATE operation updates only the large fields, DTS does not synchronize the operation.
  • CREATE TABLE
    Note If a CREATE TABLE operation creates a partitioned table or a table that contains functions, DTS does not synchronize the operation.
  • ALTER TABLE operations, including only ADD COLUMN, DROP COLUMN, and RENAME COLUMN
  • DROP TABLE
  • RENAME TABLE, TRUNCATE TABLE, and CREATE INDEX

Billing

Migration type Task configuration fee Internet traffic fee
Schema migration and full data migration Free of charge. Charged only when data is migrated from Alibaba Cloud over the Internet. For more information, see Pricing.
Incremental data migration Charged. For more information, see Pricing.

Permissions required for database accounts

Database Schema migration Full data migration Incremental data migration
Self-managed SQL Server database The SELECT permission The SELECT permission The permissions of the sysadmin role
ApsaraDB RDS for SQL Server instance The read and write permissions The read and write permissions The read and write permissions

For more information about how to create and authorize a database account, see the following topics:

Process of incremental data migration

To prevent data migration failures caused by dependencies among objects, DTS migrates the schemas and data from the source SQL Server database in the following order:

  1. Migrate the schemas of tables, views, synonyms, user-defined types, rules, defaults, and plan guides.
  2. Perform full data migration.
  3. Migrate the schemas of SQL stored procedures, SQL functions, triggers, and foreign keys.
  4. Perform incremental data migration.
    Note During schema migration and full data migration, we recommend that you do not perform data definition language (DDL) operations on the source objects. Otherwise, the objects may fail to be migrated.

Before you begin

Before you configure a data migration task, configure log settings on the self-managed SQL Server database.

  1. Run the following command in the self-managed SQL Server database to change the recovery model to full:
    use master;
    GO
    ALTER DATABASE <database_name> SET RECOVERY FULL WITH ROLLBACK IMMEDIATE;
    GO

    Parameters:

    <database_name>: the name of the source database.

    Example:

    use master;
    GO
    ALTER DATABASE mytestdata SET RECOVERY FULL WITH ROLLBACK IMMEDIATE;
    GO
  2. Run the following command to create a logical backup for the source database. Skip this step if you have already created a logical backup.
    BACKUP DATABASE <database_name> TO DISK='<physical_backup_device_name>';
    GO

    Parameters:

    • <database_name>: the name of the source database.
    • <physical_backup_device_name>: the storage path and file name of the backup file.

    Example:

    BACKUP DATABASE mytestdata TO DISK='D:\backup\dbdata.bak';
    GO
  3. Run the following command to back up the log entries of the source database:
    BACKUP LOG <database_name> to DISK='<physical_backup_device_name>' WITH init;
    GO

    Parameters:

    • <database_name>: the name of the source database.
    • <physical_backup_device_name>: the storage path and file name of the backup file.

    Example:

    BACKUP LOG mytestdata TO DISK='D:\backup\dblog.bak' WITH init;
    GO
  4. Create a clustered index for each source table. For more information, see Create Clustered Indexes.

Procedure

  1. Log on to the DTS console.
  2. In the left-side navigation pane, click Data Migration.
  3. At the top of the Migration Tasks page, select the region where the destination RDS instance resides. Select a region
  4. In the upper-right corner of the page, click Create Migration Task.
  5. Configure the source and destination databases. Configure the source and destination databases
    Section Parameter Description
    N/A Task Name DTS automatically generates a task name. We recommend that you specify an informative name for easy identification. You do not need to use a unique task name.
    Source Database Instance Type Select an instance type based on the deployment of the source database. In this example, select User-Created Database with Public IP Address.
    Note If you select other instance types, you must deploy the network environment for the source database. For more information, see Preparation overview.
    Instance Region If the instance type is set to User-Created Database with Public IP Address, you do not need to specify the Instance Region parameter.
    Note If a whitelist is configured for the self-managed SQL Server database, you must add the CIDR blocks of DTS servers to the whitelist of the database. You can click Get IP Address Segment of DTS next to Instance Region to obtain the CIDR blocks of DTS servers.
    Database Type Select SQLServer.
    Hostname or IP Address Enter the endpoint that is used to connect to the self-managed SQL Server database. In this example, enter the public IP address.
    Port Number Enter the service port number of the self-managed SQL Server database. The default port number is 1433.
    Note The service port of the self-managed SQL Server database must be accessible over the Internet.
    Database Account Enter the account that is used to log on to the self-managed SQL Server database. For information about the permissions that are required for the account, see Permissions required for database accounts.
    Database Password Enter the password of the database account.
    Note After you specify the source database parameters, click Test Connectivity next to Database Password to verify whether the specified parameters are valid. If the specified parameters are valid, the Passed message appears. If the Failed message appears, click Check next to Failed. Modify the source database parameters based on the check results.
    Destination Database Instance Type Select RDS Instance.
    Instance Region Select the region where the destination RDS instance resides.
    RDS Instance ID Select the ID of the destination RDS instance.
    Database Account Enter the database account of the destination RDS instance. For information about the permissions that are required for the account, see Permissions required for database accounts.
    Database Password Enter the password of the database account.
    Note After you specify the destination database parameters, click Test Connectivity next to Database Password to verify whether the parameters are valid. If the specified parameters are valid, the Passed message appears. If the Failed message appears, click Check next to Failed. Modify the destination database parameters based on the check results.
  6. In the lower-right corner of the page, click Set Whitelist and Next.
    Note DTS adds the CIDR blocks of DTS servers to the whitelist of the destination RDS instance. This ensures that DTS servers can connect to the destination RDS instance.
  7. Select the migration types and the objects to be migrated. Select the migration types and the objects to be migrated
    Setting Description
    Select the migration types
    • To perform only full data migration, select Schema Migration and Full Data Migration.
    • To ensure service continuity during data migration, select Schema Migration, Full Data Migration, and Incremental Data Migration. In this example, select all of the three migration types.
    Note If Incremental Data Migration is not selected, do not write data to the self-managed SQL Server database during full data migration. This ensures data consistency between the source and destination databases.
    Select the objects to be migrated

    Select one or more objects from the Available section and click the Rightwards arrow icon to move the objects to the Selected section.

    Note
    • A single data migration task can migrate incremental data from only one database. To migrate incremental data from multiple databases, you must create a data migration task for each database.
    • You can select columns, tables, or databases as the objects to be migrated.
    • By default, after an object is migrated to the destination database, the name of the object remains unchanged. You can use the object name mapping feature to rename the objects that are migrated to the destination database. For more information, see Object name mapping.
    • If you use the object name mapping feature to rename an object, other objects that are dependent on the object may fail to be migrated.
    Specify whether to rename objects You can use the object name mapping feature to rename the objects that are migrated to the destination instance. For more information, see Object name mapping.
    Specify the retry time for failed connections to the source or destination database By default, if DTS fails to connect to the source or destination database, DTS retries within the next 12 hours. You can specify the retry time based on your needs. If DTS reconnects to the source and destination databases within the specified time, DTS resumes the data migration task. Otherwise, the data migration task fails.
    Note When DTS retries a connection, you are charged for the DTS instance. We recommend that you specify the retry time based on your business needs. You can also release the DTS instance at your earliest opportunity after the source and destination instances are released.
  8. Click Precheck.
    Note
    • A precheck is performed before the migration task starts. The migration task only starts after the precheck succeeds.
    • If the precheck fails, click the Note icon next to each failed check item to view the related details. Fix the issues as instructed and run the precheck again.
  9. After the task passes the precheck, click Next.
  10. In the Confirm Settings dialog box, specify the Channel Specification and select Data Transmission Service (Pay-As-You-Go) Service Terms.
  11. Click Buy and Start to start the data migration task.
    • Full data migration

      We recommend that you do not manually stop the task during full data migration. Otherwise, the data migrated to the destination instance will be incomplete. You can wait until the data migration task automatically stops.

    • Incremental data migration

      The task does not automatically stop during incremental data migration. You must manually stop the task.

      Note We recommend that you select an appropriate time to manually stop the data migration task. For example, you can stop the task during off-peak hours or before you switch your workloads to the destination instance.
      1. Wait until Incremental Data Migration and The migration task is not delayed appear in the progress bar of the migration task. Then, stop writing data to the source database for a few minutes. The delay time of incremental data migration may be displayed in the progress bar.
      2. After the status of incremental data migration changes to The migration task is not delayed again, manually stop the migration task. The migration task is not delayed
  12. Switch your workloads to the destination RDS instance.

What to do next

The database accounts that are used for data migration have the read and write permissions. After data migration is complete, you must delete the accounts of both the self-managed SQL Server database and the ApsaraDB RDS for SQL Server instance to ensure security.