This topic describes how to synchronize data from a self-managed SQL Server database to a PolarDB for MySQL cluster by using Data Transmission Service (DTS).
Prerequisites
- The version of the self-managed SQL Server database is supported by DTS. For more information, see Overview of data synchronization scenarios.
The destination PolarDB for MySQL cluster is created. For more information, see Purchase an Enterprise Edition cluster and Purchase a subscription cluster.
The available storage space of the PolarDB for MySQL cluster is larger than the total size of the data in the self-managed SQL Server database.
If the source ApsaraDB RDS for SQL Server instance meets one of the following conditions, we recommend that you split the synchronization task into multiple subtasks:
The source instance contains more than 10 databases.
A single database of the source instance backs up its logs at an interval of less than 1 hour.
A single database of the source instance executes more than 100 DDL statements each hour.
Logs are written at a rate of 20 MB/s for a single database of the source instance.
The change data capture (CDC) feature needs to be enabled for more than 1,000 tables in the source ApsaraDB RDS for SQL Server instance.
Limits
During schema synchronization, DTS synchronizes foreign keys from the source database to the destination database.
During full data synchronization and incremental data synchronization, DTS temporarily disables the constraint check and cascade operations on foreign keys at the session level. If you perform the cascade update and delete operations on the source database during data synchronization, data inconsistency may occur.
Limit type | Description |
Limits on the source database |
|
Other limits |
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Special cases | If the source instance is an ApsaraDB RDS for SQL Server instance, DTS automatically creates an account named |
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 many-to-one synchronization
For more information about the synchronization topologies that are supported by DTS, see Synchronization topologies.
SQL operations that can be synchronized
Operation type | SQL statement |
DML | INSERT, UPDATE, and DELETE |
DDL |
Note
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Preparations
Before you configure a data synchronization task, configure log settings and create clustered indexes on the self-managed SQL Server database.- Execute the following statement on the self-managed SQL Server database to change the recovery model to full. You can also change the recovery model by using SQL Server Management Studio (SSMS). For more information, see View or Change the Recovery Model of a Database (SQL Server).
Parameter:use master; GO ALTER DATABASE <database_name> SET RECOVERY FULL WITH ROLLBACK IMMEDIATE; GO
<database_name>: the name of the source database.
Example:use master; GO ALTER DATABASE mytestdata SET RECOVERY FULL WITH ROLLBACK IMMEDIATE; GO
- Execute the following statement to create a logical backup for the source database. Skip this step if you have already created a logical backup.
Parameter:BACKUP DATABASE <database_name> TO DISK='<physical_backup_device_name>'; GO
- <database_name>: the name of the source database.
- <physical_backup_device_name>: the storage path and file name of the backup file.
BACKUP DATABASE mytestdata TO DISK='D:\backup\dbdata.bak'; GO
- Execute the following statement to create a log backup for the source database.
Parameter:BACKUP LOG <database_name> to DISK='<physical_backup_device_name>' WITH init; GO
- <database_name>: the name of the source database.
- <physical_backup_device_name>: the storage path and file name of the backup file.
BACKUP LOG mytestdata TO DISK='D:\backup\dblog.bak' WITH init; GO
Procedure
Go to the Data Synchronization Tasks page.
Log on to the Data Management (DMS) console.
In the top navigation bar, click DTS.
In the left-side navigation pane, choose .
NoteOperations 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.
You can also go to the Data Synchronization Tasks page of the new DTS console.
On the right side of Data Synchronization Tasks, select the region in which the data synchronization instance resides.
NoteIf you use the new DTS console, you must select the region in which the data synchronization instance resides in the top navigation bar.
Click Create Task. In the Create Task wizard, configure the source and destination databases. The following table describes the parameters.
Section
Parameter
Description
N/A
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 an existing DMS database instance
The database instance that you want to use. You can choose whether to use an existing instance based on your business requirements.
If you select an existing instance, DTS automatically populates the parameters for the database.
If you do not select an existing instance, you must manually configure parameters for the database.
Database Type
The type of the source database. Select SQL Server.
Access Method
The access method of the source database. Select Express Connect, VPN Gateway, or Smart Access Gateway.
Instance Region
The region in which the self-managed SQL Server database resides.
NoteIf your source database is a self-managed database, you must deploy the network environment for the database. For more information, see Preparation overview.
Replicate Data Across Alibaba Cloud Accounts
Specifies whether to migrate data across Alibaba Cloud accounts. In this example, No is selected.
Connected VPC
The ID of the virtual private cloud (VPC) in which the self-managed SQL Server database is deployed.
IP address
The server IP address of the self-managed SQL Server database.
Port Number
The service port number of the self-managed SQL Server database. Default value: 1433.
Database Account
The account that is used to log on to the self-managed SQL Server database. The account must have permissions of the sysadmin role. For more information, see CREATE USER and GRANT (Transact-SQL).
Database Password
The password that is used to access the database instance.
Destination Database
Select an existing DMS database instance
The database instance that you want to use. You can choose whether to use an existing instance based on your business requirements.
If you select an existing instance, DTS automatically populates the parameters for the database.
If you do not select an existing instance, you must manually configure parameters for the database.
Database Type
The type of the destination database. Select PolarDB for MySQL.
Access Method
The access method of the destination database. Select Alibaba Cloud Instance.
Instance Region
The region in which the destination PolarDB for MySQL cluster resides.
PolarDB Cluster ID
The ID of the destination PolarDB for MySQL cluster.
Database Account
The account that is used to log on to the destination PolarDB for MySQL cluster. The account must have read and write permissions on the destination database.
Database Password
The password that is used to access the database instance.
In the lower part of the page, click Test Connectivity and Proceed.
If the source or destination database is an Alibaba Cloud database instance, such as an ApsaraDB RDS for MySQL or ApsaraDB for MongoDB instance, DTS automatically adds the CIDR blocks of DTS servers to the whitelist of the instance. If the source or destination database is a self-managed database hosted on an Elastic Compute Service (ECS) instance, DTS automatically adds the CIDR blocks of DTS servers to the security group rules of the ECS instance, and you must make sure that the ECS instance can access the database. If the database is deployed on multiple ECS instances, you must manually add the CIDR blocks of DTS servers to the security group rules of each ECS instance. If the source or destination database is a self-managed database that is deployed in a data center or provided by a third-party cloud service provider, you must manually add the CIDR blocks of DTS servers to the whitelist of the database to allow DTS to access the database. For more information, see Add the CIDR blocks of DTS servers.
WarningIf the CIDR blocks of DTS servers are automatically or manually added to the whitelist of the database or instance, or to the ECS security group rules, security risks may arise. Therefore, before you use DTS to synchronize data, you must understand and acknowledge the potential risks and take preventive measures, including but not limited to the following measures: enhancing the security of your username and password, limiting the ports that are exposed, authenticating API calls, regularly checking the whitelist or ECS security group rules and forbidding unauthorized CIDR blocks, or connecting the database to DTS by using Express Connect, VPN Gateway, or Smart Access Gateway.
Configure the objects for change tracking and advanced settings.
Parameter
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.
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.
NoteIf 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.
WarningIf 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 migration, DTS does not migrate 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 task fails. Proceed with caution.
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 or TRUNCATE 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:
Provides no intrusion to 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:
If the source database is an Amazon RDS for SQL Server instance, a Microsoft Azure SQL Server database, or a Google Cloud SQL for SQL Server instance, full and incremental data migration is supported.
You can use a native CDC component of SQL Server to obtain incremental data. This improves the stability of incremental data migration 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 migration has a latency of 10 seconds.
If you migrate multiple tables in multiple databases, stability and performance issues may occur.
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.
NoteIn this scenario, data synchronization is performed between heterogeneous databases. Therefore, only tables can be synchronized. Other objects such as views, triggers, or stored procedures are not synchronized 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.
NoteTo select the SQL operations performed on a specific database or table, right-click an object to be synchronized in the Selected Objects section. In the dialog box that appears, select the SQL operations that you want to synchronize. For more information, see SQL operations that can be synchronized.
To specify WHERE conditions to filter data, right-click an object in the Selected Objects section. In the dialog box that appears, specify the conditions. For more information about how to specify the conditions, see Specify filter conditions.
If you use the object name mapping feature to rename an object, other objects that are dependent on the object may fail to be synchronized.
Click Next: Advanced Settings to configure advanced settings.
Parameter
Description
Monitoring and Alerting
Specifies whether to configure alerting for the data synchronization task. 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 contacts. For more information, see Configure monitoring and alerting when you create a DTS task.
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.
NoteIf 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 the 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 The wait time before a retry when other issues occur in the source and destination databases parameter must be smaller than the value of the Retry Time for Failed Connection parameter.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.
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.
NoteBefore 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.
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 instance. 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.
NoteThis parameter is available only if you select the Subscription billing method.
Read and select the 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.