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

Prerequisites

  • The version of the self-managed SQL Server database is supported by DTS. For more information, see Overview of data migration scenarios.
  • The destination ApsaraDB RDS for SQL Server instance is created. For more information, see Create an ApsaraDB RDS for SQL Server instance.
  • 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.
  • If the source database is in the following conditions, we recommend that you migrate data by using the backup feature of ApsaraDB RDS for SQL Server. For more information, see Migrate data from a self-managed database to ApsaraDB RDS for SQL Server.
    • 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.
    • The logs of a database in the source ApsaraDB RDS for SQL Server instance involve heap tables, tables without primary keys, compressed tables, or tables with computed columns. You can execute the following SQL statements to check whether the source database contains these tables.
      1. Execute the following SQL statement to check for heap tables:
        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);
      2. Execute the following SQL statement to 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');
      3. Execute the following SQL statement to check for primary key columns contained in clustered index 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 WHERE t.type= 'U' AND s.name NOT IN('cdc', 'sys')  AND t.name NOT IN('systranschemas')  AND t.object_id IN (SELECT pk_columns.object_id AS object_id 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_columns LEFT JOIN (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 ON pk_columns.object_id= cluster_colums.object_id WHERE pk_columns.column_id != cluster_colums.column_id);
      4. Execute the following SQL statement to check for compressed tables:
        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;
      5. Execute the following SQL statement to check for tables with 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);

Usage notes

Category Description
Limits on the source database
  • The server to which the source database belongs must have sufficient outbound bandwidth. Otherwise, the data migration speed is affected.
  • 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 tables, such as renaming tables or columns in the destination database, 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 in batches, 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 need to migrate more than 10 databases, we recommend that you configure multiple tasks to migrate the databases in batches. Otherwise, the performance and stability of your data migration task may be compromised.
  • If you need 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 logical backup must be performed.
    • If you perform only incremental data migration, the data logs of the source database must be stored 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 stored for at least seven days. Otherwise, DTS may fail to obtain the data logs and the task may fail. In exceptional circumstances, data inconsistency or loss may 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 to be migrated in 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 Enterprise Edition, you must use SQL Server 2008 or later.
    • If the source database is of Standard Edition, you must use SQL Server 2016 SP1 or later.
    • If the source database is of Standard Edition or Enterprise Edition and its version is SQL Server 2017, we recommend that you update the version.
  • Limits on operations to be performed on the source database:
    • During schema migration 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 data to the source database during data migration. Otherwise, data inconsistency between the source and destination databases may occur. To ensure data consistency, we recommend that you select schema migration, full data migration, and incremental data migration as the migration types.
Other limits
  • DTS does not migrate data of the following types: CURSOR, ROWVERSION, SQL_VARIANT, HIERACHYID, and GEOMETRY.
  • If you select Incremental Synchronization Based on Logs of Source Database as SQL Server Incremental Synchronization Mode in the Configure Objects and Advanced Settings step, the tables to be migrated must have clustered indexes that contain primary key columns. In addition, the table to be migrated cannot be compressed tables or contain computed columns. Ignore the preceding limits if the hybrid log parsing mode is used.
  • If you migrate data between different versions of databases, make sure that the database versions are compatible.
  • In the Incremental Synchronization Based on Logs of Source Database mode, DTS adds a heartbeat table named dts_log_heart_beat to the source database to ensure that the latency of data migration is accurate. In the 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 some tables.
  • 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 and destination databases. This may increase the loads on the database servers.
  • 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.
  • Make sure that the precision settings for columns of the FLOAT or DOUBLE data type meet your business requirements. DTS uses the ROUND(COLUMN,PRECISION) function to retrieve values from columns of the FLOAT or DOUBLE data type. If you do not specify a precision, DTS sets the precision for the FLOAT data type to 38 digits and the precision for the DOUBLE data type to 308 digits.
  • DTS attempts to resume data migration tasks that failed within the last seven days. Before you switch workloads to the destination database, stop or release the data migration task. You can also execute the REVOKE statement to revoke the write permissions from the accounts used by DTS to access the destination database. Otherwise, the data in the source database overwrites the data in the destination database after the task is resumed.
  • If the data migration task involves incremental data migration, DTS does not allow you to perform the reindexing operation. If you perform the reindexing operation, the data migration task may fail, or even data loss may occur.
  • If the number of CDC-enabled tables to be migrated in a single migration task exceeds 1,000, the precheck fails.
  • To perform incremental data migration, you must disable the trigger and foreign keys in the destination database. Otherwise, the data migration task fails.
Special cases If the destination instance is an ApsaraDB RDS for SQL Server instance, take note of the following limits:

DTS automatically creates a destination database in the ApsaraDB RDS for SQL Server instance. However, if the name of the database to be migrated does not conform to the naming conventions of ApsaraDB RDS, you must manually create a database in the destination ApsaraDB RDS for SQL Server instance before you configure the data migration task. For more information, see Create a database on an ApsaraDB RDS for SQL Server instance.

Billing

Migration type Instance 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 Billing overview.
Incremental data migration Charged. For more information, see Billing overview.

Migration types

  • Schema migration

    DTS migrates the schemas of objects from the source database 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.
    • DTS does not migrate the schemas of 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.
  • Full data migration

    DTS migrates the historical data of objects from the source database to the destination database.

  • Incremental data migration

    After full data migration is complete, DTS migrates incremental data from the source database to the destination database. Incremental data migration allows you to ensure service continuity when you migrate data between self-managed databases.

SQL operations that can be migrated during incremental data migration

Operation type SQL statement
DML INSERT, UPDATE, and DELETE
Note If an UPDATE operation updates only the large fields, DTS does not migrate the operation.
DDL
  • CREATE TABLE
    Note If a CREATE TABLE operation creates a partitioned table or a table that contains functions, DTS does not migrate the operation.
  • ALTER TABLE

    ADD COLUMN and DROP COLUMN

  • DROP TABLE
  • CREATE INDEX and DROP INDEX
Note
  • Transactional DDL statements cannot be migrated.
  • DTS does not migrate DDL operations that contain user-defined types.
  • If the source database uses the mixed log-based parsing mode, all common DDL operations can be migrated.

Permissions required for database accounts

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

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

Data migration process

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.

Preparations

Note Before you configure a task to migrate incremental data, you must configure log settings on the self-managed SQL Server database and create clustered indexes.
Warning If you want to migrate incremental data from multiple databases, repeat Steps 1 to 4 for each database.
  1. Execute the following statement on 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. Execute the following statement 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. Execute the following statement 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

Procedure

  1. Go to the Data Migration Tasks page.
    1. Log on to the Data Management (DMS) console.
    2. In the top navigation bar, click DTS.
    3. In the left-side navigation pane, choose DTS (DTS) > Data Migration.
    Note You can also configure the settings by using the new DTS console.
  2. From the drop-down list to the right of Data Migration Tasks, select the region in which your data migration instance resides.
    Note If you use the new DTS console, select the region in which your data migration instance resides in the upper-left corner.
  3. Click Create Task. On the page that appears, configure the source and destination databases.
    Warning After you select the source and destination instances, we recommend that you read the limits displayed at the top of the page. This helps you create and run the data migration task.
    Section Parameter Description
    N/A Task Name

    The name of the task. DTS automatically generates a task name. We recommend that you specify a descriptive name to identify the task. You do not need to specify a unique task name.

    Source Database Select Instance
    The instance that you want to use. You can choose whether to use an existing instance based on your business requirements.
    • If you use an existing instance, DTS automatically applies the parameter settings of the instance.
    • If you do not use an existing instance, you must set 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 Public IP Address.
    Note If your source database is a self-managed database, you must deploy the network environment for the database. For more information, see Preparation overview.
    Instance Region The region in which the self-managed SQL Server database resides.
    Hostname or IP address The endpoint that is used to access to the self-managed SQL Server database. In this example, a public IP address is used.
    Port Number The service port number of the self-managed SQL Server database. The default port number is 1433.
    Database Account The database 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

    The password of the database account.

    Destination Database Select Instance
    The instance that you want to use. You can choose whether to use an existing instance based on your business requirements.
    • If you use an existing instance, DTS automatically applies the parameter settings of the instance.
    • If you do not use an existing instance, you must set parameters for the database.
    Database Type The type of the destination database. Select SQL Server.
    Access Method The access method of the destination database. Select Alibaba Cloud Instance.
    Instance Region The region in which the destination ApsaraDB RDS for SQL Server instance resides.
    RDS Instance ID The ID of the destination ApsaraDB RDS for SQL Server instance.
    Database Account The database account of the destination ApsaraDB RDS for SQL Server instance. For more information about the permissions that are required for the account, see Permissions required for database accounts.
    Database Password

    The password of the database account.

  4. If a whitelist is configured for your self-managed database, add the CIDR blocks of DTS servers to the whitelist. Then, click Test Connectivity and Proceed.
    Warning
    • 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 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. For more information, see Add the CIDR blocks of DTS servers to the security settings of on-premises databases. 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 whitelist of the database to allow DTS to access the database.
    • If the CIDR blocks of DTS servers are automatically or manually added to the whitelist of the database, Alibaba Cloud database instance, or ECS security group rules, 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 ECS security group rules and forbidding unauthorized CIDR blocks, or connecting the database to DTS by using Express Connect, VPN Gateway, or Smart Access Gateway.
    • After the DTS task is complete or released, we recommend that you manually detect and remove the added CIDR blocks from the whitelist of the database, Alibaba Cloud database instance, or ECS security group rules.
  5. Select objects for the task and configure advanced settings.
    Parameter Description
    Task Stages
    • 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.
    Note If Incremental Data Migration is not selected, we recommend that you do not write data to the source instance during data migration. This ensures data consistency between the source and destination instances.
    Processing Mode of Conflicting Tables
    • Precheck and Report Errors: checks whether the destination database contains tables that have the same names as tables in the source database. If the source and destination databases do not contain identical table names, the precheck is passed. Otherwise, an error is returned during the precheck and the data migration task cannot be started.

      Note You can use the object name mapping feature to rename the tables that are migrated to the destination database. You can use this feature if the source and destination databases contain identical table names and the tables in the destination database cannot be deleted or renamed. 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 potential risks.
      • If the source and destination databases have the same schema, DTS does not migrate data records that have the same primary keys as data records in the destination database.
      • If the source and destination databases have different schemas, only specific columns are migrated or the data migration task fails.
    SQL Server Incremental Synchronization Mode
    • Log-based Parsing for Non-heap Tables and CDC-based Incremental Synchronization for Heap Tables:
      • Advantages:
        • Supports heap tables, tables without primary keys, compressed tables, and tables with computed columns.
        • Provides higher stability and a variety of complete DDL statements.
      • Disadvantages:

        DTS creates the trigger dts_cdc_sync_ddl, the heartbeat table dts_sync_progress, and the DDL storage table dts_cdc_ddl_history in the source database and enables Change Data Capture (CDC) for the source database and specific tables.

    • Incremental Synchronization Based on Logs of Source Database:
      • Advantages:

        Provides no intrusion to the source database.

      • Disadvantages:

        Does not support heap tables, tables without primary keys, compressed tables, or tables with computed columns.

    Source Objects

    Select one or more objects from the Source Objects section and click the Rightwards arrow icon to add the objects to the Selected Objects section.

    Note You can select columns, tables, or schemas as the objects to be migrated. If you select tables or columns as the objects to be migrated, DTS does not migrate other objects such as views, triggers, or stored procedures 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 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
    • 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.
    • 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 about the procedure, see Use SQL conditions to filter data.
    • To select the SQL operations performed on a specific database or table, right-click an object in the Selected Objects section. In the dialog box that appears, select the SQL operations that you want to migrate. For more information, see SQL operations that can be migrated during incremental data migration.
  6. Click Next: Advanced Settings to configure advanced settings.
    Parameter Description
    Set Alerts
    Specifies whether to set alerts for the data migration task. If the task fails or the migration latency exceeds the threshold, the alert contacts will receive notifications. Valid values:
    • No: does not set alerts.
    • Yes: sets alerts. If you select Yes, you must also set the alert threshold and alert contacts.
    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 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 reconnects 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 set different retry time ranges for multiple data migration tasks that have the same source or destination database, the shortest retry time range that is set 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 your earliest opportunity after the source and destination instances are released.
    Configure ETL
    Specifies whether to configure the extract, transform, and load (ETL) feature. For more information, see What is ETL? Valid values:
  7. In the lower part of the page, click Next: Save Task Settings and Precheck.
    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 result, troubleshoot the issues. Then, run a precheck again.
    • If an alert is triggered for an item during the precheck, click Confirm Alert Details next to the item and analyze the causes.
      • You can troubleshoot the issues based on the causes and run a precheck again.
      • If you do not need to troubleshoot the issues, 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.
  8. Wait until the Success Rate becomes 100%. Then, click Next: Purchase Instance.
  9. On the Purchase Instance page, specify the Instance Class parameter for the data migration instance. The following table describes the parameter.
    Section Parameter Description
    New Instance Class Instance Class

    DTS provides several instance classes that have different performance in migration speed. You can select an instance class based on your business scenario. For more information, see Specifications of data migration instances.

  10. Read and select Data Transmission Service (Pay-as-you-go) Service Terms.
  11. Click Buy and Start to start the data migration task. You can view the progress of the task in the task list.