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Migrate RDS for SQL Server to SelectDB

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ApsaraDB for SelectDB supports sub-second responses for massive data queries, tens of thousands of concurrent point queries, and high throughput for complex analytics. Data Transmission Service (DTS) lets you migrate SQL Server databases to ApsaraDB for SelectDB. This example uses an ApsaraDB RDS for SQL Server instance as the source.

Note

This feature is in closed beta.

Scenarios

  • You have a source RDS SQL Server instance and a target ApsaraDB for SelectDB instance.

  • Consider splitting the migration into multiple tasks if your source instance meets any of the following conditions:

    • The source instance has more than 10 databases.

    • Log backups are performed more than once per hour for a single database.

    • More than 100 Data Definition Language (DDL) operations are performed per hour on a single database.

    • The log generation rate for a single database exceeds 20 MB/s.

    • You must enable change data capture (CDC) on more than 1,000 tables.

Limitations

Note

During schema migration, DTS does not migrate foreign keys from the source database to the target database.

Type

Description

Source database limitations

  • The source database server must have sufficient outbound bandwidth. Insufficient bandwidth reduces data migration speed.

  • The tables to be migrated must have a primary key or unique constraint, and the columns in the key or constraint must be unique. Otherwise, data duplication may occur in the destination database.

  • If you select specific tables for migration and need to edit them (for example, map table or column names), a single migration task can migrate a maximum of 1,000 tables. If you exceed this limit, the task fails upon submission. Split the tables into multiple tasks or configure a task to migrate the entire database.

  • A single migration task supports a maximum of 10 databases. Exceeding this limit may cause stability and performance issues. Split the migration into multiple tasks if needed.

  • If you configure a task to migrate specific objects instead of an entire database, you cannot migrate objects that have the same table name but different schema names to the same destination database within a single task.

  • If you perform incremental data migration, the transaction logs must meet the following requirements:

    • Transaction logging must be enabled, the backup mode must be set to Full, and a full physical backup must have been successfully performed.

    • For incremental-only data migration, Data Transmission Service (DTS) requires retaining source database transaction logs for more than 24 hours. If a task includes both full and incremental data migration, retain logs for at least seven days. After full data migration is complete, you can reduce the retention period to more than 24 hours. Otherwise, the DTS task may fail due to unavailable transaction logs. In extreme cases, data inconsistency or loss may occur. Issues caused by insufficient log retention are not covered by the DTS Service Level Agreement (SLA).

  • If you enable CDC (change data capture) for the source tables to be migrated, they must meet the following conditions. Otherwise, the precheck will fail.

    • 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, the database owner must be sa. If the source database is an ApsaraDB 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 it to a later version.

  • DTS uses the fn_log function to obtain logs from the source database. This function has performance bottlenecks, so do not clear source database logs prematurely. Otherwise, the DTS task may fail.

  • Limits on operations in the source database:

    • During the schema migration and full data migration phases, do not perform DDL operations that change the database or table structure. Otherwise, the data migration task will fail.

    • If you perform only full data migration, do not write new data to the source instance. Otherwise, data in the source and destination databases becomes inconsistent. To ensure real-time data consistency, select Schema Migration, Full Data Migration, and Incremental Data Migration.

  • If the source database is a read-only instance, DTS does not migrate DDL operations.

  • If the source database is an Azure SQL Database, a migration instance can migrate only one database.

  • If the source database is an ApsaraDB RDS for SQL Server instance and the migration task includes incremental data migration, ensure that Transparent Data Encryption (TDE) is disabled for task stability. For more information, see Disable TDE.

  • If you use the sp_rename command to rename objects such as stored procedures before the schema migration task runs, the task may not work as expected or may fail.

    Note

    Use the ALTER command to rename database objects.

  • In hybrid log-based parsing mode, the source database does not support consecutive column add or drop operations with an interval of less than 10 minutes. For example, if you run the following SQL statements consecutively, the task will fail.

    ALTER TABLE test_table DROP COLUMN Flag;
ALTER TABLE test_table ADD Remark nvarchar(50) not null default('');

  • If the source database is an ApsaraDB RDS for SQL Server instance that runs the Web edition, 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, enable the READ_COMMITTED_SNAPSHOT parameter for the source database to prevent shared lock contention from affecting data writes. Otherwise, data inconsistency or task failure may occur. Issues caused by not enabling this parameter are not covered by the DTS SLA.

Other limitations

  • Currently, you can migrate data only to tables that use the Unique engine in a SelectDB instance. Ensure that all unique keys in the target table also exist in the source table and are included in the migration objects. Otherwise, data inconsistency may occur.

  • Requirements for migration objects:

    • Schema initialization is supported for databases, schemas, and tables.

    • DTS does not support migrating data with the following data types: CURSOR, ROWVERSION, SQL_VARIANT, HIERARCHYID, POLYGON, GEOMETRY, GEOGRAPHY, and user-defined types created with the CREATE TYPE command.

    • DTS does not support migrating the following objects: PROCEDURE, FUNCTION, TRIGGER, DATATYPE, SYNONYM, CATALOG, PLAN_GUIDE, and SEQUENCE.

  • If you set Configure Objects to SQL Server Incremental Synchronization Mode in the Incremental Synchronization Based on Logs of Source Database (Heap tables are not supported) step, the tables to be migrated must have a clustered index that includes the primary key column. DTS does not support migrating heap tables, tables without primary keys, compressed tables, tables with computed columns, or tables with sparse columns in this mode. These limitations do not apply in hybrid log-based parsing mode.

  • If you set Configure Objects to SQL Server Incremental Synchronization Mode in the Log-based Parsing for Non-heap Tables and CDC-based Incremental Synchronization for Heap Tables (Hybrid Log-based Parsing) step, the following limits also apply:

    • DTS relies on the CDC component for incremental migration. Ensure that the CDC job in the source database is running as expected. Otherwise, the DTS task will fail.

    • By default, the CDC component stores incremental data for three days. Adjust the retention period by running the exec console.sys.sp_cdc_change_job @job_type = 'cleanup', @retention= <time>; command.

      Note

      • <time> specifies the retention period in minutes.

      • If the average number of daily incremental SQL changes for a single table exceeds 10 million, set <time> to 1440.

    • In a single migration task, enable CDC for no more than 1,000 tables. Otherwise, the task may experience high latency or become unstable.

    • The precheck module for a DTS incremental data migration task enables CDC in the source database. During this process, the SQL Server engine's internal limitations may cause temporary table locking in the source database.

  • If you set Configure Objects to SQL Server Incremental Synchronization Mode in the Polling and querying CDC instances for incremental synchronization step, the following limits also apply:

    • The source database account used by the DTS instance must have the permissions to enable CDC. An account with the sysadmin role is required to enable database-level CDC. A privileged account is required to enable table-level CDC.

      Note

      • The most privileged account (server administrator) provided by the Azure SQL Database console meets the requirements. For databases purchased based on the vCore model, CDC can be enabled for all specifications. For databases purchased based on the DTU model, CDC can be enabled only for service tiers of S3 or higher.

      • The privileged account of an Amazon RDS for SQL Server instance meets the requirements and supports enabling database-level CDC via stored procedures.

      • CDC cannot be enabled for tables that have a clustered columnstore index.

      • The precheck module for a DTS incremental data migration task enables CDC in the source database. During this process, the SQL Server engine's internal limitations may cause temporary table locking in the source database.

    • DTS obtains incremental data by polling and querying the CDC instance of each table in the source database. Migrate no more than 1,000 tables from the source database. Otherwise, the task may experience high latency or become unstable.

    • By default, the CDC component stores incremental data for three days. Adjust the retention period by running the exec console.sys.sp_cdc_change_job @job_type = 'cleanup', @retention= <time>; command.

      Note

      • <time> specifies the retention period in minutes.

      • If the average number of daily incremental SQL changes for a single table exceeds 10 million, set <time> to 1440.

    • Consecutive column add or drop operations are not supported (more than two ADD COLUMN or DROP COLUMN DDL operations within one minute). Otherwise, the task may fail.

    • Do not modify the CDC instances of the source database. Otherwise, the data migration task may fail or data loss may occur.

  • When you configure parameters in the Selected Objects box, only the bucket_count (number of buckets) parameter is currently supported.

    Note

    The value of the bucket_count parameter must be a positive integer. The default value is auto.

  • Do not create a new cluster in the target SelectDB instance during data migration, or the task will fail. You may be able to restore a failed task by restarting the migration instance.

  • SelectDB instances support only database and table names that start with a letter. If the name of a database or table to be migrated does not start with a letter, you must use the mapping feature to rename it.

  • If the name of an object to be migrated (database, table, or column) contains Chinese characters, you must use the mapping feature to rename it (for example, to an English name). Otherwise, the task may fail.

  • DTS does not support migrating DDL operations that modify multiple columns at once or perform consecutive modifications on the same table.

  • Do not add backend (BE) nodes to the SelectDB database during data migration, or the task will fail. You may be able to restore a failed task by restarting the migration instance.

  • Before data migration, evaluate the performance of the source and target databases and plan to migrate during off-peak hours. Full data initialization consumes read and write resources on both databases, which may increase the database load.

  • Full data initialization runs INSERT operations in parallel, which can cause table fragmentation in the target database. After full data initialization, the tablespace of the target instance is larger than that of the source instance.

  • During data migration, only DTS can write data to the target database. Otherwise, data will become inconsistent between the source and target databases.

  • DTS does not support migrating complex DDL operations.

  • If the number of CDC-enabled tables in a single migration task exceeds the value set in the The maximum number of tables for which CDC is enabled that DTS supports. parameter, the precheck fails.

  • If a migration task includes incremental data migration, you cannot perform re-indexing operations. This may cause the task to fail or result in data loss.

    Note

    You cannot modify the primary key of a table for which CDC is enabled.

  • Do not perform index rebuild operations on the migration instance. This can cause the task to fail or result in data loss.

    Note

    Primary key changes are not supported on CDC-enabled tables.

  • If a task includes incremental migration and a single field in a CDC-enabled table to be written contains more than 64 KB of data, run the exec sp_configure 'max text repl size', -1; command to adjust the source database configuration in advance.

    Note

    By default, a CDC job can process a maximum data size of 64 KB for a single field.

  • If a DDL write to the target database fails, the DTS task continues to run. You must check the task log for the failed DDL. For more information about how to view task logs, see View task logs.

  • For multiple migration instances that use the same SQL Server database as the source, the incremental data capture modules work independently of each other.

  • During incremental migration, DTS uses a batch-and-sync strategy, writing data no more than once every 5 seconds by default. The typical steady-state latency is under 10 seconds. You can adjust this interval by setting the selectdb.reservoir.timeout.milliseconds parameter to 1,000–10,000 milliseconds.

  • If a task fails, DTS support staff will attempt to restore it within eight hours. During restoration, they may restart the task or adjust its parameters.

    Note

    Only DTS task parameters are modified—not database parameters. Parameters that may be adjusted include those listed in Modify instance parameters.

  • DTS does not support partially rolled-back transactions on the source, and these rollback operations may be lost.

  • Because SQL Server is a closed-source database, its log format can have unpredictable characteristics that cause issues during incremental Change Data Capture (CDC) parsing. Before you enable incremental synchronization or migration from a SQL Server source in production, we strongly recommend a comprehensive PoC test covering all business change scenarios, schema adjustments, and peak-hour stress tests. The business logic used in production must be consistent with that of the PoC test.

Special case

If the source is an ApsaraDB RDS for SQL Server instance, DTS creates a system account named rdsdt_dtsacct on the 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.

Billing

Migration type

Link configuration fee

Public network traffic

Schema migration and full data migration

No charge.

No charge in this example.

Note

Public network traffic fees apply if the Access Method for the destination database is set to Public IP Address. For more information, see billing overview.

Incremental data migration

Charges apply. For more information, see billing overview.

Supported SQL

Type

SQL statement

DML

INSERT, UPDATE, DELETE

DDL

ALTER TABLE (ADD COLUMN and DROP COLUMN only)

Database account privileges

Database

Schema migration

Full migration

Incremental migration

Source RDS SQL Server

Owner privileges

Owner privileges

Owner privileges

Destination SelectDB

Cluster access privilege (Usage_priv) and the following database privileges: Select_priv, Load_priv, Alter_priv, Create_priv, and Drop_priv.

To create and grant privileges to a database account:

Procedure

  1. 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.

  2. Click Create Task to navigate to the task configuration page.

  3. Configure the source and destination databases.

    Category

    Parameter

    Description

    N/A

    Task Name

    DTS automatically generates a task name. We recommend that you specify a descriptive name for easy identification. The name does not need to be unique.

    Source Database

    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.

    Access Method

    Select Alibaba Cloud Instance.

    Instance Region

    Select the region where the source RDS SQL Server instance resides.

    Replicate Data Across Alibaba Cloud Accounts

    This example shows data migration between instances in the same Alibaba Cloud account. Select No.

    Instance ID

    Select the instance ID of the source RDS SQL Server instance.

    Database Account

    Enter the database account for the source RDS SQL Server instance. For information about permission requirements, see Permission requirements for database accounts.

    Database Password

    Enter the password for the specified database account.

    Destination Database

    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 SelectDB.

    Access Method

    Select Alibaba Cloud Instance.

    Instance Region

    Select the region where the destination SelectDB instance resides.

    Replicate Data Across Alibaba Cloud Accounts

    This example shows data migration between instances in the same Alibaba Cloud account. Select No.

    Instance ID

    Select the instance ID of the destination SelectDB instance.

    Database Account

    Enter the database account for the destination SelectDB instance. For information about permission requirements, see Permission requirements for database accounts.

    Database Password

    Enter the password for the database account.

  4. After completing the configuration, click Test Connectivity and Proceed at the bottom of the page.

    Note

    • Ensure that you add the CIDR blocks of the DTS servers (either automatically or manually) to the security settings of both the source and destination databases to allow access. For more information, see Add the IP address whitelist of DTS servers.

    • If the source or destination is a self-managed database (i.e., the Access Method is not Alibaba Cloud Instance), you must also click Test Connectivity in the CIDR Blocks of DTS Servers dialog box.

  5. Configure the task objects.

    1. On the Configure Objects page, configure the objects that you want to migrate.

      Parameter

      Description

      Migration Types

      • If you only need to perform a full data migration, select both Schema Migration and Full Data Migration.

      • If you need to perform a migration with minimal downtime, select Schema Migration, Full Data Migration, and Incremental Data Migration.

      Important

      • When you migrate data from SQL Server to SelectDB, DTS converts the data types. If you do not select Schema Migration, you must create Unique model tables with the required schema in the destination SelectDB instance in advance. For more information, see Data type mappings.

      • If you do not select Incremental Data Migration, do not write new data to the source instance during migration to ensure data consistency.

      Schema Mapping Mode of Source and Destination Databases

      SQL Server uses a three-level hierarchy (database > schema > table), whereas SelectDB uses a two-level hierarchy (database > table), so you must map the source and destination database structures. This migration link supports only the Exclude Schema Names of Source Databases mode, where the source database name maps to the destination database name and the source table name maps to the destination table name.

      Important

      In this mode, tables in different schemas of the source database cannot have the same name. Otherwise, the DTS task may fail or data inconsistency may occur.

      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 with source database heap tables, tables without primary keys, compressed tables, and tables with computed columns.

          • High link stability. This mode can obtain complete DDL statements and supports a wide range of DDL scenarios.

        • 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. It also enables database-level Change Data Capture (CDC) and partial table CDC.

          • You cannot execute SELECT INTO, TRUNCATE, and RENAME COLUMN statements on tables for which CDC is enabled in the source database. Triggers created by DTS in the source database cannot be manually deleted.

      • Incremental Synchronization Based on Logs of Source Database (Heap tables are not supported):

        • Advantages:

          This mode is non-intrusive to the source database.

        • Disadvantages:

          Does not support scenarios with source database 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 synchronization 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.

          • Uses the native SQL Server CDC component to obtain incremental data, which makes incremental synchronization more stable and uses less network bandwidth.

        • Disadvantages:

          • The source database account used by the DTS instance must have the permission to enable CDC. Incremental data synchronization has a latency of about 10 seconds.

          • In scenarios involving synchronization of multiple databases and tables, there may be risks of stability and performance issues.

      The maximum number of tables for which CDC is enabled that DTS supports.

      This setting limits the number of tables on which CDC can be enabled within the current synchronization instance. The default value is 1,000.

      Note

      This parameter is not available if you set SQL Server Incremental Synchronization Mode to Incremental Synchronization Based on Logs of Source Database (Heap tables are not supported).

      Processing Mode of Conflicting Tables

      • Precheck and Report Errors: DTS checks whether a table with the same name exists in the destination database. If not, the precheck passes. If a table with the same name exists, an error is reported during the precheck phase, and the data migration task does not start.

        Note

        If you cannot delete or rename the table with the same name in the destination database, you can change the name of the table in the destination database by using name mapping. For more information, see Map schema, table, and column names.

      • Ignore Errors and Proceed: DTS skips the check for tables with the same name in the destination database.

        Warning

        Selecting Ignore Errors and Proceed may lead to data inconsistency and business risks. For example:

        • If the table schemas are the same, and a record in the destination database has the same primary key value as a record in the source database, the record from the source database overwrites the record in the destination database.

        • If the table schemas are different, only partial data may be migrated, or the migration may fail. Use this option with caution.

      Capitalization of Object Names in Destination Instance

      You can configure the case sensitivity policy for the names of migrated objects, such as databases, tables, and columns, in the destination instance. By default, DTS default policy is selected. You can also choose to keep the case sensitivity consistent with the default policy of the source or destination database. For more information, see Case sensitivity of object names in the destination database.

      Source Objects

      In the Source Objects box, click the objects to migrate, and then click Right arrow to move them to the Selected Objects box.

      Note

      You can select objects at the database or table level.

      Selected Objects

      • To rename a migration object in the destination instance, right-click the object in the Selected Objects pane. For more information, see Map schema, table, and column names.

      • If Migration Types is set to Schema Migration, you have selected tables to migrate, and you need to set the number of buckets (the bucket_count parameter), right-click a table in the Selected Objects list. In the Parameter Settings area, set Enable Parameter Settings to Yes, set the Value based on your requirements, and then click OK.

      Note

      • To select the SQL operations for incremental migration at the database or table level, right-click the object in the Selected Objects pane and select the desired SQL operations in the dialog box.

      • To filter data by using a WHERE clause, right-click the table to be migrated in the Selected Objects pane and set the filter condition in the dialog box. For more information, see Set filter conditions.

      • If you use the object name mapping feature, the migration of other objects that depend on the mapped object may fail.

    2. Click Next: Advanced Settings to configure advanced parameters.

      Parameter

      Description

      Dedicated Cluster for Task Scheduling

      By default, DTS schedules tasks on a shared cluster. You do not need to select one. If you want more stable tasks, you can purchase a dedicated cluster to run DTS migration tasks.

      Retry Time for Failed Connections

      After the migration task starts, if the connection to the source or destination database fails, DTS reports an error and immediately begins to retry the connection. The default retry duration is 720 minutes. You can customize the retry time to a value from 10 to 1440 minutes. We recommend that you set the duration to more than 30 minutes. If DTS reconnects to the source and destination databases within the specified duration, the migration task automatically resumes. Otherwise, the task fails.

      Note

      • For multiple DTS instances that share the same source or destination, the network retry time is determined by the setting of the last created task.

      • Because you are charged for the task during the connection retry period, we recommend that you customize the retry time based on your business needs, or release the DTS instance as soon as possible after the source and destination database instances are released.

      Retry Time for Other Issues

      After the migration task starts, if a non-connectivity issue, such as a DDL or DML execution exception, occurs in the source or destination database, DTS reports an error and immediately begins to retry the operation. The default retry duration is 10 minutes. You can customize the retry time to a value from 1 to 1440 minutes. We recommend that you set the duration to more than 10 minutes. If the related operations succeed within the specified retry duration, the migration task automatically resumes. Otherwise, the task fails.

      Important

      The value of Retry Time for Other Issues must be less than the value of Retry Time for Failed Connections.

      Enable Throttling for Full Data Migration

      During full migration, DTS consumes read and write resources on the source and destination databases, which may increase the database load. If required, you can enable throttling for the full migration task. You can set Queries per second (QPS) to the source database, RPS of Full Data Migration, and Data migration speed for full migration (MB/s) to reduce the load on the destination database.

      Note

      • This configuration item is available only if you select Full Data Migration for Migration Types.

      • You can also adjust the full migration speed after the migration instance is running.

      Enable Throttling for Incremental Data Migration

      If required, you can also choose to set speed limits for the incremental migration task. You can set RPS of Incremental Data Migration and Data migration speed for incremental migration (MB/s) to reduce the load on the destination database.

      Note

      • This configuration item is available only if you select Incremental Data Migration for Migration Types.

      • You can also adjust the incremental migration speed after the migration instance is running.

      Environment Tag

      You can select an environment tag to identify the instance. This step is not required in this example.

      Configure ETL

      Based on your business needs, select whether to configure the ETL feature to process data.

      • Yes: Configures the ETL feature. You must also enter data processing statements in the text box.

      • No: Does not configure the ETL feature.

      Monitoring and Alerting

      Select whether to set alerts and receive alert notifications based on your business needs.

      • No: Does not set an alert.

      • Yes: Configure alerts by setting an alert threshold and an alert contact. If a migration fails or the latency exceeds the threshold, the system sends an alert notification.

    3. Optional: After you finish the configuration, click Next: Configure Database and Table Fields to set the Primary Key Column, Distribution Key, and Engine for the tables to be migrated in the destination database. For this migration link, the Engine can only be set to unique.

      Note

      • This step appears only if Migration Types is selected as a Schema Migration. You can set Definition Status to All to make modifications.

      • For the Primary Key Column, you can select multiple columns to form a composite primary key. You must also select one or more columns from the Primary Key Column as the Distribution Key.

  6. 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.

  7. Purchase the instance.

    1. When the Success Rate is 100%, click Next: Purchase Instance.

    2. 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?

      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.

    3. After the configuration is complete, read and select Data Transmission Service (Pay-as-you-go) Service Terms.

    4. 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.

Data type mappings

Category

SQL Server type

SelectDB type

Numeric

BIT

INT

TINYINT

SMALLINT

SMALLINT

SMALLINT

INT

INT

BIGINT

BIGINT

DECIMAL

DECIMAL

NUMERIC

DECIMAL

FLOAT

DOUBLE

REAL

DOUBLE

MONEY

STRING

SMALLMONEY

STRING

Date and time

DATE

DATEV2

DATETIME

DATETIMEV2

DATETIME2[(fsp)]

DATETIMEV2

SMALLDATETIME

DATETIMEV2

TIME[(fsp)]

STRING

DATETIMEOFFSET[(fsp)]

DATETIMEV2

TIMESTAMP

STRING

String

  • CHAR

  • VARCHAR

VARCHAR(4×N)

Important

To prevent data loss, the CHAR(n) and VARCHAR(n) data types are mapped to VARCHAR(4*n) in SelectDB.

  • If no data length is specified, the default is VARCHAR(65533).

  • If the data length exceeds 65533, the data type is mapped to STRING.

  • NCHAR

  • NVARCHAR

VARCHAR(4×N)

Important

To prevent data loss, the NCHAR(n) and NVARCHAR(n) data types are mapped to VARCHAR(4*n) in SelectDB.

  • If no data length is specified, the default is VARCHAR(65533).

  • If the data length exceeds 65533, the data type is mapped to STRING.

  • VARCHAR(MAX)

  • NVARCHAR(MAX)

  • TEXT

  • NTEXT

STRING

  • BINARY

  • VARBINARY

  • IMAGE

STRING

XML

STRING

UNIQUEIDENTIFIER

STRING
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