Use DTS to synchronize RDS for SQL Server to DataHub-Data Transmission Service(DTS)-阿里云帮助中心

Prerequisites

A source RDS SQL Server instance is created. For more information, see Quickly create and use an RDS SQL Server instance.

Important
For a list of supported source instance versions, see Synchronization solution overview.
You have activated the DataHub service and created a Project to receive synchronized data. For more information, see Quick Start (Synchronization Example) and Project operations.
We recommend splitting a synchronization task into multiple tasks if the 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.

Notes

Note

DTS does not synchronize foreign keys from the source database to the destination database. Therefore, cascading operations on the source database are not synchronized to the destination database.

Type	Description
Source database limits	Tables to be synchronized must have a primary key or a UNIQUE constraint, and the fields must be unique. Otherwise, duplicate data may appear in the destination database. If you synchronize data at the table level, need to edit objects such as mapping column names, and the number of tables in a single task exceeds 5,000, split the tables into multiple tasks. You can also configure a task to synchronize the entire database. Otherwise, an error may be reported after you submit the task. A single sync task supports a maximum of 10 databases. If you exceed this limit, you risk stability and performance issues. In this case, split the tables and configure them in multiple tasks. When you configure a task to synchronize specific objects to the same destination database, you cannot select objects that have the same table name but different schema names. DTS uses the `fn_log` function to get logs from the source database. This function has performance bottlenecks. Do not clear the source database logs too early, or the task may fail. Data logs: Data logs must be enabled. The backup mode must be set to Full, and a full physical backup must have been successfully performed. For incremental synchronization tasks, DTS requires the source database to retain data logs for more than 24 hours. For tasks that include both full and incremental synchronization, DTS requires the source database to retain data logs for at least 7 days. After the full synchronization is complete, you can change the log retention period to more than 24 hours. If the retention period is too short, the DTS task may fail because it cannot get the data logs. In extreme cases, this can cause data inconsistency or data loss. Issues caused by setting a log retention period shorter than required by DTS are not covered by the DTS Service-Level Agreement (SLA). If Change Data Capture (CDC) needs to be enabled for tables 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 must be the same as the return value of the `SERVERPROPERTY` function. If the source database is a self-managed SQL Server instance, the database owner must be `sa`. If the source database is an RDS for SQL Server instance, the database owner must be `sqlsa`. If the source database is Enterprise Edition, it must be SQL Server 2008 or later. If the source database is Standard Edition, it must be SQL Server 2016 SP1 or later. If the source database is SQL Server 2017 (Standard or Enterprise Edition), upgrade the version. If the source database is an Azure SQL Database, a single sync instance can synchronize only one database. If the source database is an RDS for SQL Server instance, ensure that the Transparent Data Encryption (TDE) feature is disabled to ensure the stability of the sync instance. For more information, see Disable TDE. If you use the `sp_rename` command to modify the names of objects, such as stored procedures, in the source database before a schema synchronization task runs, the task may produce unexpected results or fail. Note We recommend using the `ALTER` command to rename database objects. In hybrid log parsing mode, you cannot consecutively run multiple operations to add or drop columns in the source database within a 10-minute interval. For example, running the following SQL statements consecutively causes the task to report an error. `ALTER TABLE test_table DROP COLUMN Flag; ALTER TABLE test_table ADD Remark nvarchar(50) not null default('');` During the schema synchronization phase, do not run DDL operations that change the database or table structure. Otherwise, the data synchronization task will fail. We recommend that you keep the `READ_COMMITTED_SNAPSHOT` transaction processing mode parameter of the source database enabled while a full data sync task is running. This prevents shared locks from affecting data writes. Otherwise, issues such as data inconsistency or instance failures may occur. Such issues are not covered by the DTS Service-Level Agreement (SLA).
Other limits	Only incremental data synchronization and schema synchronization are supported. Full data synchronization is not supported. The maximum length for a single String field in the destination DataHub is 2 MB. Requirements for synchronization objects: The following objects support initial schema synchronization: Schema, Table, View, Function, and Procedure. Warning Because this scenario involves data synchronization between heterogeneous databases, data types may not map one-to-one. This can cause task failures or data loss. Carefully evaluate how data type mapping affects your business. For more information, see Data type mapping for initial schema synchronization. Initial schema synchronization is not supported for the following structural objects: assemblies, service broker, full-text indexes, full-text catalogs, distributed schemas, distributed functions, CLR stored procedures, CLR scalar functions, CLR table-valued functions, internal tables, system tables, and aggregate functions. Data of the following data types cannot be synchronized: CURSOR, ROWVERSION, SQL_VARIANT, HIERARCHYID, POLYGON, GEOMETRY, GEOGRAPHY, and user-defined types created with the `CREATE TYPE` command. Tables that contain computed columns cannot be synchronized. The following objects cannot be synchronized: INDEX, VIEW, PROCEDURE, FUNCTION, TRIGGER, FK, INDEX, FULL_TEXT_INDEX, DATATYPE, DEFAULT, SYNONYM, CATALOG, PLAN_GUIDE, DEFAULT_CONSTRAINT, UK, CK, and SEQUENCE. To ensure accurate latency for incremental data synchronization, DTS performs the following actions: In the "parse source logs for incremental synchronization" mode, DTS creates the dts_cdc_sync_ddl trigger, the dts_sync_progress heartbeat table, and the dts_cdc_ddl_history DDL storage table in the source database. In hybrid incremental synchronization mode, DTS creates the dts_cdc_sync_ddl trigger, the dts_sync_progress heartbeat table, and the dts_cdc_ddl_history DDL storage table, and also enables database-level CDC and CDC for some tables. The data change volume for tables with CDC enabled in the source database should not exceed 1,000 records per second (RPS). Evaluate the performance of the source and destination databases before you synchronize data. Synchronize data during off-peak hours. Otherwise, the initial full data synchronization consumes read and write resources on both databases, which may increase the database load. Initial full synchronization runs concurrent INSERT operations, which causes table fragmentation in the destination database. As a result, the tablespace of the destination instance is larger than that of the source instance after the initial full synchronization is complete. During DTS synchronization, do not write data to the destination database from any source other than DTS. This will cause data inconsistency between the source and destination databases. For example, if you use DMS to perform online DDL operations while data is being written to the destination database from another source, data loss may occur in the destination database. Reindexing is not supported for a sync instance. This operation can cause the task to fail or even lead to data loss. Note Changes related to the primary key are not supported for tables with CDC enabled. If the number of tables with CDC enabled in a single sync task exceeds 1,000, the precheck fails. If a single field in a table with CDC enabled needs to store more than 64 KB of data, you must run the `exec sp_configure 'max text repl size', -1;` command in advance to adjust the configuration of the source database. Note By default, a CDC job can process a maximum of 64 KB for a single field. To use the feature to modify synchronized objects, you cannot remove a database. If multiple sync instances use the same SQL Server database as the source, their incremental data ingestion modules are independent of each other. 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. SQL Server is a commercial, closed-source database. Its log format has characteristics that can cause unavoidable issues when DTS performs incremental CDC and parsing. Before you use DTS for incremental or migration synchronization from a SQL Server source in a production environment, perform a comprehensive proof of concept (POC). Your POC should cover all business change types, table schema adjustments, and peak-hour stress tests. The SQL Server log format can be unpredictable. To ensure that DTS runs efficiently and stably, make sure your production business logic is consistent with what you tested in the POC.
Special cases	If the source instance is an RDS for SQL Server instance, DTS creates a `rdsdt_dtsacct` account in the source instance for data synchronization. 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

Synchronization type	Pricing
Schema synchronization and full data synchronization	Free of charge.
Incremental data synchronization	Charged. For more information, see Billing overview.

Synchronization topologies

One-way one-to-one synchronization
One-way one-to-many synchronization
One-way many-to-one synchronization

For more information, see Synchronization topologies.

Supported SQL operations

Type	SQL statement
DML	`INSERT`, `UPDATE`, `DELETE` Note DTS does not synchronize `UPDATE` statements that only update a large field.

Database account permissions

Database	Permissions	Actions
ApsaraDB RDS for SQL Server instance	Owner permissions for the objects to be synchronized.	Create standard, privileged, and global read-only accounts and Modify the permissions of an account.

Procedure

Go to the data synchronization task list page in the destination region. You can do this in one of two ways.
DTS console
1. Log on to the DTS console.
2. In the navigation pane on the left, click Data Synchronization.
3. In the upper-left corner of the page, select the region where the synchronization instance is located.
DMS console
Note
The actual steps may vary depending 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 DMS console.
2. In the top menu bar, choose Data + AI > DTS (DTS) > Data Synchronization.
3. To the right of Data Synchronization Tasks, select the region of the synchronization instance.
Click Create Task to open the task configuration page.

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	Select the registered database instance with DTS from the drop-down list. The database information below is automatically configured. Note In the DMS console, this configuration item is Select a DMS database instance. If you have not registered the database instance 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 of the source ApsaraDB RDS for SQL Server instance.
	Replicate Data Across Alibaba Cloud Accounts	This example involves synchronizing data within the same Alibaba Cloud account. Select No.
	RDS Instance ID	Select the ID of the source ApsaraDB RDS for SQL Server instance.
	Database Account	Enter the database account for the source ApsaraDB RDS for SQL Server instance. For information about the required permissions, see Permissions required for database accounts.
	Database Password	Enter the password for the specified database account.
	Encryption	Select Non-encrypted or SSL-encrypted. If SSL encryption is not enabled for the source database, select Non-encrypted. If SSL encryption is enabled for the source database, select SSL-encrypted. DTS trusts the server certificate by default.
Destination Database	Select Existing Connection	Select the registered database instance with DTS from the drop-down list. The database information below is automatically configured. Note In the DMS console, this configuration item is Select a DMS database instance. If you have not registered the database instance or do not need to use a registered instance, manually configure the database information below.
	Database Type	Select DataHub.
	Access Method	Select Alibaba Cloud Instance.
	Instance Region	Select the region of the destination DataHub instance.
	Project	Select the destination DataHub Project.

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.

Configure the task objects.

On the Configure Objects page, specify the objects to synchronize.

Parameter	Description
Synchronization Types	Incremental Data Synchronization is selected by default. You must also select Schema Synchronization.
Processing Mode of Conflicting Tables	Precheck and Report Errors: Checks for tables with the same names in the destination database. If any tables with the same names are found, an error is reported during the precheck and the data synchronization task does not start. Otherwise, the precheck is successful. Note If you cannot delete or rename the table with the same name in the destination database, you can map it to a different name in the destination. For more information, see Database Table Column Name Mapping. Ignore Errors and Proceed: Skips the check for tables with the same name in the destination database. Warning Selecting Ignore Errors and Proceed may cause data inconsistency and put your business at risk. For example: If the table schemas are consistent and a record in the destination database has the same primary key or unique key value as a record in the source database: During full data synchronization, DTS retains the destination record and skips the source record. During incremental synchronization, DTS overwrites the destination record with the source record. If the table schemas are inconsistent, data initialization may fail. This can result in only partial data synchronization or a complete synchronization failure. Use with caution.
Naming Rules of Additional Columns	When DTS synchronizes data to DataHub, it adds additional columns to the destination topic. If the names of these additional columns conflict with existing column names in the destination topic, the data synchronization task fails. You must select New Rule or Previous Rule for the Naming Rules of Additional Columns. Warning Before you select an additional column rule, evaluate whether the additional columns will conflict with existing columns in the destination topic. Otherwise, the task may fail or data may be lost. For more information about the rules and definitions of additional columns, see Names and definitions of additional columns.
Case Policy for Destination Object Names	Configure the case-sensitivity policy for database, table, and column names in the destination instance. By default, the DTS default policy is selected. You can also choose to use the default policy of the source or destination database. For more information, see Case policy for destination object names.
Source Objects	In the Source Objects box, click the objects, and then click to move them to the Selected Objects box. Note You can select objects at the database, table, or column level. If you select only tables or columns, DTS does not synchronize other object types (such as views, triggers, and stored procedures).
Selected Objects	To rename a single object in the destination instance, right-click the object in the Selected Objects box. For more information, see Map a single object name. To rename multiple objects in bulk, click Batch Edit in the upper-right corner of the Selected Objects box. For more information, see Map multiple object names in bulk. Note To select which SQL operations to synchronize at the schema or table level, right-click an object in the Selected Objects box and make your selections. To set WHERE conditions to filter data, right-click a table in the Selected Objects box and specify the conditions. For more information, see Set filter conditions. If you use the object name mapping feature, other objects that depend on the renamed object might fail to be synchronized.

Click Next: Advanced Settings.

Parameter	Description
Dedicated Cluster for Task Scheduling	By default, DTS uses a shared cluster for tasks, so you do not need to make a selection. For greater task stability, you can purchase a dedicated cluster to run the DTS synchronization task. For more information, see What is a DTS dedicated cluster?.
Retry Time for Failed Connections	If the connection to the source or destination database fails after the synchronization task starts, 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 1,440 minutes. We recommend a duration of 30 minutes or more. If the connection is restored within this period, the task resumes automatically. Otherwise, the task fails. Note If multiple DTS instances (e.g., Instance A and B) share a source or destination, DTS uses the shortest configured retry duration (e.g., 30 minutes for A, 60 for B, so 30 minutes is used) for all instances. DTS charges for task runtime during connection retries. Set a custom duration based on your business needs, or release the DTS instance promptly after you release the source/destination instances.
Retry Time for Other Issues	If a non-connection issue (e.g., a DDL or DML execution error) occurs, DTS reports an error and immediately retries the operation. The default retry duration is 10 minutes. You can also customize the retry time to a value from 1 to 1,440 minutes. We recommend a duration of 10 minutes or more. If the related operations succeed within the set retry time, the synchronization task automatically resumes. Otherwise, the task fails. Important The value of Retry Time for Other Issues must be less than that of Retry Time for Failed Connections.
Enable Throttling for Incremental Data Synchronization	You can also limit the incremental synchronization rate to reduce pressure on the destination database by setting RPS of Incremental Data Synchronization and Data synchronization speed for incremental synchronization (MB/s).
Environment Tag	You can select an environment tag to identify the instance. In this example, you do not need to select a tag.
Configure ETL	Choose whether to enable the extract, transform, and load (ETL) feature. For more information, see What is ETL? Valid values: Yes: Enables the ETL feature. Enter data processing statements in the code editor. For more information, see Configure ETL in a data migration or data synchronization task. No: Disables the ETL feature.
Monitoring and Alerting	Choose whether to set up alerts. If the synchronization fails or the latency exceeds the specified threshold, DTS sends a notification to the alert contacts. No: No alerts are configured. Yes: Configures alerts. You must also set the alert threshold and alert contact. For more information, see Configure monitoring and alerting during task configuration.

Save the task and perform a precheck.
- To view the parameters for configuring this instance via an API operation, hover over the Next: Save Task Settings and Precheck button and click Preview OpenAPI parameters in the tooltip.
- If you have finished viewing the API parameters, click Next: Save Task Settings and Precheck at the bottom of the page.
Note
- Before a synchronization task starts, DTS performs a precheck. You can start the task only if the precheck passes.
- If the precheck fails, click View Details next to the failed item, fix the issue as prompted, and then rerun the precheck.
- If the precheck generates warnings:
  For non-ignorable warning, click View Details next to the item, fix the issue as prompted, and run the precheck again.
  For ignorable warnings, you can bypass them by clicking Confirm Alert Details, then Ignore, and then OK. Finally, click Precheck Again to skip the warning and run the precheck again. Ignoring precheck warnings may lead to data inconsistencies and other business risks. Proceed with caution.

Purchase the instance.

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

On the Purchase page, select the billing method and link specifications for the data synchronization instance. For more information, see the following table.

Category	Parameter	Description
New Instance Class	Billing Method	Subscription: You pay upfront for a specific duration. This is cost-effective for long-term, continuous tasks. Pay-as-you-go: You are billed hourly for actual usage. This is ideal for short-term or test tasks, as you can release the instance at any time to save costs.
	Resource Group Settings	The resource group to which the instance belongs. The default is default resource group. For more information, see What is Resource Management?.
	Instance Class	DTS offers synchronization specifications at different performance levels that affect the synchronization rate. Select a specification based on your business requirements. For more information, see Data synchronization link specifications.
	Subscription Duration	In subscription mode, select the duration and quantity of the instance. Monthly options range from 1 to 9 months. Yearly options include 1, 2, 3, or 5 years. Note This option appears only when the billing method is Subscription.

Read and select the checkbox for Data Transmission Service (Pay-as-you-go) Service Terms.
Click Buy and Start, and then click OK in the OK dialog box.
You can monitor the task progress on the data synchronization page.