synchronization between sql server databases - Data Transmission Service

You can use Data Transmission Service (DTS) to synchronize data between ApsaraDB RDS for SQL Server instances.

Prerequisites

The source and destination ApsaraDB RDS for SQL Server instances have been created. For more information about supported database versions, see Overview of data synchronization scenarios. For more information about how to create an ApsaraDB RDS for SQL Server instance, see Create an ApsaraDB RDS for SQL Server instance.
Important
The following source databases are supported in hybrid log parsing mode when the SQL Server Incremental Synchronization Mode is set to Log-based Parsing For Non-heap Tables And CDC-based Incremental Synchronization For Heap Tables:
- Self-managed SQL Server or ApsaraDB RDS for SQL Server database of the Enterprise or Enterprise Evaluation edition: version 2012, 2014, 2016, or 2019.
- Self-managed SQL Server or ApsaraDB RDS for SQL Server database of the Standard edition: version 2016 or 2019.
The available storage space in the destination RDS SQL Server instance must be greater than the total size of the data in the source RDS SQL Server instance.

If you synchronize data from a self-managed SQL Server database to an ApsaraDB RDS for SQL Server instance and one of the following conditions is met, we recommend that you synchronize data using the backup feature of ApsaraDB RDS for SQL Server. For more information, see Migrate data from a self-managed database to an ApsaraDB RDS for SQL Server instance.

The source instance contains more than 10 databases.
A single database of the source instance backs up its logs more than once per hour.
A single database of the source instance executes more than 100 DDL statements per hour.
Logs are written at a rate of more than 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.

The logs of a database in the source instance contain heap tables, tables without primary keys, compressed tables, or tables with computed columns. You can run the following SQL statements to check whether the source database contains these types of tables:

Check for heap tables in the source database:

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);

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');

Check for primary key columns that are not included in clustered index columns in the source database:

SELECT s.name schema_name, t.name 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_colums_counter.object_id AS object_id FROM (select pk_colums.object_id, sum(pk_colums.column_id) column_id_counter 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_colums group by object_id) pk_colums_counter inner JOIN ( select cluster_colums.object_id, sum(cluster_colums.column_id) column_id_counter 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.index_id = 1) cluster_colums group by object_id ) cluster_colums_counter ON pk_colums_counter.object_id = cluster_colums_counter.object_id and pk_colums_counter.column_id_counter != cluster_colums_counter.column_id_counter);

Check for compressed tables in the source database:

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;

Check for tables that contain 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);

Check for tables that contain sparse 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_sparse = 1);

Precautions

Note

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

Limit type	Description
Limits on the source database	The tables to be synchronized 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 synchronized and you want to edit the tables in the destination database, such as renaming tables or columns, you can synchronize up to 5,000 tables in a single data synchronization task. If you run a task to synchronize more than 5,000 tables, a request error occurs. In this case, we recommend that you configure multiple tasks to synchronize the tables or configure a task to synchronize the entire database. A single data synchronization task can synchronize data from up to 10 databases. If you want to synchronize data from more than 10 databases, we recommend that you configure multiple tasks to synchronize the data. Otherwise, the performance and stability of your data synchronization task may be compromised. DTS does not synchronize tables for memory optimization. DTS uses the fn_log function to obtain logs of the source database. However, this function has performance bottlenecks. Therefore, we recommend that you do not clear the logs of the source database before the task is complete. Otherwise, the task may fail. The following requirements for data logs must be met: The data logging feature must be enabled. The backup mode must be set to Full and full physical backup must be performed. If you perform only incremental data synchronization, the data logs of the source database must be retained for more than 24 hours. If you perform both full data synchronization and incremental data synchronization, the data logs of the source database must be retained for at least seven days. Otherwise, DTS may fail to obtain the data logs and the task may fail. In some cases, data inconsistency or loss may even occur. After full data synchronization 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 reliability or performance stated in the service level agreement (SLA) of DTS may not be guaranteed. If CDC needs to be enabled for the tables to be synchronized from the source database, make sure that the tables meet the following requirements. Otherwise, the precheck fails. The value of the srvname field in the sys.sysservers view is the same as the return value of the SERVERPROPERTY function. If the source database is a self-managed SQL Server database, the database owner must be the sa user. If the source database is an ApsaraDB RDS for SQL Server database, the database owner must be the sqlsa user. If the source database is of the Enterprise edition, you must use SQL Server 2008 or later. If the source database is of the Standard edition, you must use SQL Server 2016 SP1 or later. If the source database is of the Standard or Enterprise edition and its version is SQL Server 2017, we recommend that you update the version. If the source database is a read-only instance, you cannot synchronize DDL operations. If the source database is an Azure SQL Database, a data synchronization task can synchronize data from only one database. If the source database is an RDS SQL Server, disable the Transparent Data Encryption (TDE) feature to ensure the stability of a data synchronization task. For more information, see the Disable TDE section in the topic "Configure TDE". In hybrid log-based parsing mode, you cannot perform multiple operations to add columns to or remove columns from the source database within 10 minutes. For example, if you execute the following SQL statements within 10 minutes, an error is reported for the task. `ALTER TABLE test_table DROP COLUMN Flag; ALTER TABLE test_table ADD Remark nvarchar(50) not null default('');` During schema synchronization and full data synchronization, do not execute DDL statements to change the schemas of databases or tables. Otherwise, the data synchronization task fails. If the source database is an ApsaraDB RDS for SQL Server instance that runs SQL Server Web edition, you must set the SQL Server Incremental Synchronization Mode parameter to Incremental Synchronization Based on Logs of Source Database (Heap tables are not supported) when you configure the task. We recommend that you use the `READ_COMMITTED_SNAPSHOT` parameter of transaction processing mode in the source database during full data synchronization. This can prevent the impact of shared lock on data writes. If you do not set the parameter, the exceptions such as inconsistent data and instances that fail to run occur. Issues that arise in such circumstances are not covered by the service level agreement (SLA) of DTS.
Other limits	DTS does not synchronize the following types of data: CURSOR, ROWVERSION, SQL_VARIANT, HIERARCHYID, POLYGON, GEOMETRY, and GEOGRAPHY. If you synchronize data between different versions of databases, make sure that the database versions are compatible. If you set the SQL Server Incremental Synchronization Mode parameter to Incremental Synchronization Based on Logs of Source Database (Heap tables are not supported) in the Configure Objects step, the tables to be synchronized must have clustered indexes that contain primary key columns. The tables to be synchronized cannot be heap tables, tables without primary keys, compressed tables, or tables with computed columns. Ignore the preceding limits in the hybrid log-based parsing mode. Note For more information about how to view table information, see the How do I view the information about heap tables, tables without primary keys, compressed tables, and tables that contain computed columns in an SQL Server database? section of the FAQ topic. If you set the SQL Server Incremental Synchronization Mode parameter to Log-based Parsing for Non-heap Tables and CDC-based Incremental Synchronization for Heap Tables (Hybrid Log-based Parsing) in the Configure Objects step, take note of the following limits: DTS uses the CDC component to synchronize incremental data. Make sure that the CDC job in the source database runs as expected. Otherwise, the DTS task fails. The CDC component can store the incremental data for 3 days by default. You can adjust the retention period by running the `exec console.sys.sp_cdc_change_job @job_type = 'cleanup', @retention= <time>;` command. Note `<time>` indicates the retention time. Unit: minutes. If the average daily number of the incremental data in the SQL Server database exceeds 10 million, we recommend setting the `<time>` parameter to 1,440. The pre-module of an incremental data migration task in DTS enables database-level and table-level CDC in the source database. In this process, locked tables that lasts a few seconds occurs in the source database due to the limit of SQL Server database. We recommend that you specify a data synchronization task that contains no more than 1,000 tables for which CDC is enabled. Otherwise, the task may be delayed or unstable. If you set the SQL Server Incremental Synchronization Mode parameter to Polling and querying CDC instances for incremental synchronization in the Configure Objects step, the following limits apply: The source database account used by the DTS instance must have the permissions to enable the CDC feature. To enable database-level CDC, you must use an account that is assigned the sysadmin role. To enable table-level CDC, you must use a privileged account. Note A server administrator account of a database in Microsoft Azure SQL Database has the required permissions. CDC can be enabled for all databases that are purchased in Azure SQL Database based on the vCore model. CDC can be enabled for databases that are purchased in Azure SQL Database based on the database transaction unit (DTU) model only if the databases have a service tier of S3 or greater. A privileged account of an Amazon RDS for SQL Server instance has the required permissions. CDC can be enabled for stored procedures at the database level. CDC cannot be enabled for clustered columnstore indexes. The pre-module of an incremental data synchronization task in DTS enables database-level and table-level CDC in the source database. In this process, locked tables that lasts a few seconds occurs in the source database due to the limit of SQL Server database. DTS obtains incremental data by performing round-robin queries on the CDC instance of each table in the source database. Therefore, the number of tables to be migrated from the source database cannot exceed 1,000. Otherwise, the data migration task may be delayed or unstable. The CDC component can store the incremental data for 3 days by default. You can adjust the retention period by running the `exec console.sys.sp_cdc_change_job @job_type = 'cleanup', @retention= <time>;` command. Note `<time>` indicates the retention time. Unit: minutes. If the average daily number of the incremental data in the SQL Server database exceeds 10 million, we recommend setting the `<time>` parameter to 1,440. You cannot execute a DDL statement to add or remove columns more than twice within a minute. Otherwise, the data migration task may fail. During data migration, you cannot modify the CDC instances of the source database. Otherwise, the data migration task may fail or data loss may occur. In Incremental Synchronization Based on Logs of Source Database mode, DTS creates a trigger named dts_cdc_sync_ddl, a heartbeat table named dts_sync_progress, and a DDL history table named dts_cdc_ddl_history in the source database to ensure that the latency of data synchronization is accurate. In hybrid log-based parsing incremental synchronization mode, DTS creates a trigger named dts_cdc_sync_ddl, a heartbeat table named dts_sync_progress, and a DDL history table named dts_cdc_ddl_history and enables CDC for the source database and specific tables. We recommend that you set the maximum number of records per second to 1,000 for the tables for which CDC is enabled in the source database. Before you synchronize data, evaluate the impact of data synchronization on the performance of the source and destination databases. We recommend that you synchronize data during off-peak hours. During initial full data synchronization, 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 synchronization, concurrent INSERT operations cause fragmentation in the tables of the destination database. After full data synchronization is complete, the size of the used tablespace of the destination database is larger than that of the source database. Data inconsistency between the source and destination databases occurs if data from other sources is written to the destination database during data synchronization. For example, if you use Data Management (DMS) to execute online DDL statements while data from other sources is written to the destination database, data loss may occur in the destination database. If the data synchronization task involves incremental data synchronization, DTS does not allow you to perform the reindexing operation. If you perform the reindexing operation, the data synchronization task may fail and data loss may occur. Note DTS cannot synchronize DDL operations related to the primary key of a table for which change data capture (CDC) is enabled. If the number of tables for which CDC is enabled in a data synchronization task is greater than the maximum number of tables for which CDC is enabled that DTS supports, the precheck fails. If the data of a single field that is written to the tables for which CDC is enabled exceeds 64 KB, you must use the `exec sp_configure 'max text repl size', -1;` command to configure the source database. Note By default, the maximum length of a single field in a CDC job that can be processed is 64 KB. To perform incremental data synchronization, you must disable the triggers and foreign keys in the destination database. Otherwise, the data synchronization task fails. When you modify the objects to be synchronized, you cannot remove databases. The incremental data collection modules of multiple data synchronization instances that share a source SQL Server database are independent of each other. If a DTS task fails to run, DTS technical support will try to restore the task within 8 hours. During the restoration, the task may be restarted, and the parameters of the task may be modified. Note Only the parameters of the DTS task may be modified. The parameters of databases are not modified. The parameters that may be modified include but are not limited to the parameters in the "Modify instance parameters" section of the Modify the parameters of a DTS instance topic.
Special cases	If the source instance is an ApsaraDB RDS for SQL Server instance, DTS automatically creates an account named `rdsdt_dtsacct` on the ApsaraDB RDS for SQL Server instance. This account is used for data synchronization. Do not delete this account or change the password of this account when your data synchronization task is running. Otherwise, the task may fail. For more information, see System accounts.

Billing

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

Supported synchronization topologies

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

For more information about different synchronization topologies, see Synchronization topologies.

SQL operations that can be synchronized

Operation type	SQL statement
DML	INSERT, UPDATE, DELETE Note DTS does not synchronize UPDATE statements that only update large objects.
DDL	CREATE TABLE Note Partitions and functions inside table definitions are not supported. ALTER TABLE Only ADD COLUMN and DROP COLUMN are supported. DROP TABLE CREATE INDEX, DROP INDEX Note Transactional DDL operations cannot be synchronized. For example, a single SQL statement that adds multiple columns or a single SQL statement that contains both DDL and DML operations may cause data loss. DDL operations that contain custom types cannot be synchronized. Online DDL operations cannot be synchronized. DDL operations that use a reserved keyword as a property name cannot be synchronized. DDL operations executed by system stored procedures cannot be synchronized. TRUNCATE TABLE operations cannot be synchronized.

Procedure

Use one of the following methods to go to the Data Synchronization page and select the region in which the data synchronization instance resides.
DTS console
1. Log on to the DTS console.
2. In the left-side navigation pane, click Data Synchronization.
3. In the upper-left corner of the page, select the region in which the data synchronization task resides.
DMS console
Note
The actual operations may vary based on the mode and layout of the DMS console. For more information, see Simple mode and Customize the layout and style of the DMS console.
1. Log on to the DMS console.
2. In the top navigation bar, move the pointer over Data + AI and choose DTS (DTS) > Data Synchronization.
3. From the drop-down list to the right of Data Synchronization Tasks, select the region in which the data synchronization instance resides.
Click Create Task to go to the task configuration page.

Configure the source and destination databases. The following table describes the parameters.

Warning

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

Category	Configuration	Description
None	Task Name	The name of the DTS task. DTS automatically generates a task name. We recommend that you specify a descriptive name that makes it easy to identify the task. You do not need to specify a unique task name.
Source Database	Select Existing Connection	If you use a database instance that is registered with DTS, select the instance from the drop-down list. DTS automatically populates the following database parameters for the instance. For more information, see Manage database connections. Note In the DMS console, you can select the database instance from the Select a DMS database instance drop-down list. If you fail to register the instance with DTS, or you do not need to use the instance that is registered with DTS, you must configure the following database information.
	Database Type	Select SQL Server.
	Access Method	Select Cloud Instance.
	Instance Region	Select the region where the source RDS SQL Server instance is located.
	Instance ID	Select the source RDS SQL Server instance ID.
	Database Account	Enter the database account for the source RDS SQL Server instance. This account must have owner permissions for the objects to be migrated. An administrator account meets this requirement.
	Database Password	The password that is used to access the database.
	Encryption	Select Non-encrypted or SSL-encrypted based on your scenario. If SSL encryption is not enabled for the source database, select Non-encrypted. If the source database has SSL encryption enabled, select SSL-encrypted. DTS trusts the server certificate by default.
Destination Database	Select Existing Connection	If you use a database instance that is registered with DTS, select the instance from the drop-down list. DTS automatically populates the following database parameters for the instance. For more information, see Manage database connections. Note In the DMS console, you can select the database instance from the Select a DMS database instance drop-down list. If you fail to register the instance with DTS, or you do not need to use the instance that is registered with DTS, you must configure the following database information.
	Database Type	Select SQL Server.
	Access Method	Select Cloud Instance.
	Instance Region	Select the region of the target RDS SQL Server instance.
	Instance ID	Select the target RDS SQL Server instance ID.
	Database Account	Enter the database account for the target RDS SQL Server instance. This account must have owner permissions for the objects that you want to migrate.
	Database Password	The password that is used to access the database.
	Encryption	Select Non-encrypted or SSL-encrypted as appropriate. If SSL encryption is not enabled for the destination database, select Non-encrypted. If the destination database has SSL encryption enabled, select SSL-encrypted. DTS trusts the server-side certificate by default.

Click Test Connectivity and Proceed in the lower part of the page.
Note
- Make sure that the CIDR blocks of DTS servers can be automatically or manually added to the security settings of the source and destination databases to allow access from DTS servers. For more information, see Add the CIDR blocks of DTS servers.
- If the source or destination database is a self-managed database and its Access Method is not set to Alibaba Cloud Instance, click Test Connectivity in the CIDR Blocks of DTS Servers dialog box.

Configure the objects to be synchronized.

In the Configure Objects step, configure the objects that you want to synchronize.

Configuration	Description
Synchronization Types	The synchronization types. By default, Incremental Data Synchronization is selected. You must also select Schema Synchronization and Full Data Synchronization. After the precheck is complete, DTS synchronizes the historical data of the selected objects from the source database to the destination cluster. The historical data is the basis for subsequent incremental synchronization.
Method to Migrate Triggers in Source Database	Select a method to synchronize triggers. If the objects that you want to synchronize do not include triggers, you do not need to configure this parameter. For more information, see Configure trigger synchronization or migration. Note This parameter is available only when Schema Synchronization is selected for Synchronization Types.
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: This mode supports heap tables, tables without primary keys, compressed tables, and tables with computed columns. This mode 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. You cannot execute the SELECT INTO, TRUNCATE, or RENAME COLUMN statement on tables with CDC 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 does not modify the settings of the source database. Disadvantages: This mode does not support heap tables, tables without primary keys, compressed tables, or tables with computed columns. Polling and querying CDC instances for incremental synchronization: Advantages: Full data synchronization and incremental data synchronization are supported if the source database is an Amazon RDS for SQL Server instance, a database in Microsoft Azure SQL Database, a Microsoft Azure SQL Managed Instance, a Microsoft Azure SQL Server on Virtual Machine, or a Google Cloud SQL for SQL Server instance. You can use a native CDC component of SQL Server to obtain incremental data. This improves the stability of incremental data synchronization and reduces bandwidth usage. Disadvantages: The account that DTS uses to access the source database must have the permission to enable the CDC feature. Incremental data synchronization has a latency of 10 seconds. If you configure a DTS task to synchronize multiple tables in multiple databases, stability and performance issues may occur.
The maximum number of tables for which CDC is enabled that DTS supports.	Specifies the maximum number of tables for which the current synchronization instance can enable CDC. The default value is 1000. Note This parameter is not available when SQL Server Incremental Synchronization Mode is set to Incremental Synchronization Based on Logs of Source Database (Heap tables are not supported).
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 tables that have identical table names, the precheck is passed. Otherwise, an error is returned during the precheck, and the data synchronization task cannot be started. Note If the source and destination databases contain tables with identical names and the tables in the destination database cannot be deleted or renamed, you can use the object name mapping feature to rename the tables that are synchronized to the destination database. For more information, see Map object names. Ignore Errors and Proceed: skips the precheck for identical table names in the source and destination databases. Warning If you select Ignore Errors and Proceed, data inconsistency may occur and your business may be exposed to potential risks. If the source and destination databases have the same schema and a data record in the destination database has the same primary key value or unique key value as a data record in the source database: During full data synchronization, DTS does not synchronize the data record to the destination database. The existing data record in the destination database is retained. During incremental data synchronization, DTS synchronizes the data record to the destination database. The existing data record in the destination database is overwritten. If the source and destination databases have different schemas, data may fail to be initialized. In this case, only some columns are synchronized, or the data synchronization instance fails. Proceed with caution.
Source Objects	Select one or more objects from the Source Objects section and click the icon to add the objects to the Selected Objects section. Note You can select columns, tables, or databases as objects to synchronize. If you select tables or columns as the objects to be synchronized, DTS does not synchronize other objects such as views, triggers, and stored procedures to the destination database.
Selected Objects	To rename an object that you want to synchronize to the destination instance, right-click the object in the Selected Objects section. For more information, see the "Map the name of a single object" section of the Map object names topic. To rename multiple objects at a time, click Batch Edit in the upper-right corner of the Selected Objects section. For more information, see the "Map multiple object names at a time" section of the Map object names topic. Note To select the SQL operations to synchronize at the database or table level, right-click the object in the Selected Objects section and select the desired SQL operations in the dialog box that appears. To filter data using a WHERE clause, right-click the table in the Selected Objects section and specify the filter condition in the dialog box that appears. For more information, see Set filter conditions. If you use the object name mapping feature, other objects that depend on the mapped object may fail to synchronize.

Click Next: Advanced Settings to configure advanced settings.

Configuration	Description
Dedicated Cluster for Task Scheduling	By default, DTS schedules the task to the shared cluster if you do not specify a dedicated cluster. If you want to improve the stability of data synchronization instances, purchase a dedicated cluster. For more information, see What is a DTS dedicated cluster.
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 synchronization 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 this parameter to a value greater than 30. If DTS reconnects to the source and destination databases within the specified time range, DTS resumes the data synchronization task. Otherwise, the data synchronization task fails. Note If you specify different retry time ranges for multiple data synchronization tasks that have the same source or destination database, the shortest retry time range 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.
Retry Time for Other Issues	The retry time range for other issues. For example, if the DDL or DML operations fail to be performed after the data synchronization task is started, DTS immediately retries the operations within the time range. Valid values: 1 to 1440. Unit: minutes. Default value: 10. We recommend that you set this parameter to a value greater than 10. If the failed operations are successfully performed within the specified time range, DTS resumes the data synchronization task. Otherwise, the data synchronization task fails. Important The value of the Retry Time for Other Issues parameter must be smaller than the value of the Retry Time for Failed Connections parameter.
Enable Throttling for Full Data Synchronization	During full data synchronization, DTS uses the read and write resources of the source and destination databases. This may increase the load on the database servers. You can configure the Queries per second (QPS) to the source database, RPS of Full Data Migration, and Data migration speed for full migration (MB/s) parameters for full data synchronization tasks to reduce the load on the destination database server. Note You can configure this parameter only if Full Data Synchronization is selected for the Synchronization Types parameter.
Enable Throttling for Incremental Data Synchronization	Specifies whether to enable throttling for incremental data synchronization. You can enable throttling for incremental data synchronization based on your business requirements. To configure throttling, you must configure the RPS of Incremental Data Synchronization and Data synchronization speed for incremental synchronization (MB/s) parameters. This reduces the load on the destination database server.
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	Specifies whether to enable the extract, transform, and load (ETL) feature. For more information, see What is ETL? Valid values: Yes: configures the ETL feature. You can enter data processing statements in the code editor. For more information, see Configure ETL in a data migration or data synchronization task. No: does not configure the ETL feature.
Monitoring and Alerting	Specifies whether to configure alerting for the data synchronization instance. If the task fails or the synchronization latency exceeds the specified threshold, alert contacts will receive notifications. Valid values: No: does not enable alerting. Yes: configures alerting. In this case, you must also configure the alert threshold and alert notification settings. For more information, see the "Configure monitoring and alerting when you create a DTS task" section of the Configure monitoring and alerting topic.

Click Next Step: Data Verification to configure data verification.
For more information about how to use the data verification feature, see Configure a data verification task.

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

Purchase an instance.

Wait until the Success Rate becomes 100%. Then, click Next: Purchase Instance.

On the buy page, configure the Billing Method and Instance Class parameters for the data synchronization task. The following table describes the parameters.

Section	Parameter	Description
New Instance Class	Billing Method	Subscription: You pay for a subscription when you create a data synchronization instance. The subscription billing method is more cost-effective than the pay-as-you-go billing method for long-term use. Pay-as-you-go: A pay-as-you-go instance is billed on an hourly basis. The pay-as-you-go billing method is suitable for short-term use. If you no longer require a pay-as-you-go data synchronization instance, you can release the instance to reduce costs.
	Resource Group Settings	The resource group to which the data synchronization instance belongs. Default value: default resource group. For more information, see What is Resource Management?
	Instance Class	DTS provides instance classes that vary in synchronization speed. You can select an instance class based on your business requirements. For more information, see Instance classes of data synchronization instances.
	Subscription Duration	If you select the subscription billing method, specify the subscription duration and the number of data synchronization instances that you want to create. The subscription duration can be one to nine months, one year, two years, three years, or five years. Note This parameter is available only if you select the Subscription billing method.

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

Check the status of CDC

You can use the following information to check the status of CDC or disable CDC.

Note

To use the following SQL statements, replace the variables with your actual values.

Check the status of CDC:

SELECT name, is_cdc_enabled FROM sys.databases WHERE name = '<your db name>';

Check the status of a CDC job:

SELECT database_name(database_id), job_type FROM [msdb].[dbo].[cdc_jobs] WHERE database_id = DB_ID('<your db name>');

Check whether CDC is working correctly:
- Check the disk space usage.
```
SELECT * FROM sys.dm_db_log_space_usage;
```
- Check whether the SQL Server Agent service is working as expected. For more information, see SQL Server Agent.
- Check whether CDC is scanning data as expected. If data is not scanned as expected, the DTS task may be retried or stopped.
```
SELECT * FROM sys.dm_cdc_log_scan_sessions;
```

Disable database-level CDC:

USE [<your db name>]; DROP TRIGGER [dts_cdc_sync_ddl] ON database; # Ignore if it does not exist (the trigger must be deleted first) EXECUTE [sys].[sp_cdc_disable_db];