This topic describes how to synchronize data from an ApsaraDB RDS for SQL Server instance to an ApsaraDB RDS for MySQL instance by using Data Transmission Service (DTS).

Prerequisites

  • The data synchronization instance resides in the China (Shanghai), China (Qingdao), or China East 2 Finance region.
  • The source ApsaraDB RDS for SQL Server instance is created. For more information, see Create an ApsaraDB RDS for SQL Server instance.
  • The destination ApsaraDB RDS for MySQL instance is created. For more information, see Create an ApsaraDB RDS for MySQL instance.
  • The available storage space of the ApsaraDB RDS for MySQL instance is larger than the total size of the data in the ApsaraDB RDS for SQL Server instance.

Limits

Category 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 need to edit tables (such as rename tables or columns), up to 1,000 tables can be synchronized in a single data synchronization task. If you run a task to synchronize more than 1,000 tables, a request error occurs. In this case, we recommend that you split the tables to be synchronized, configure multiple tasks to synchronize the tables, or call DTS API operations to configure tasks.
  • 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 logical backup must be performed.
    • Data logs are retained for at least 7 days during full data synchronization. You can wait until full data synchronization is complete, and then clear the data logs generated in the source database after the DTS task is run.
      Note To ensure data security, the DTS server stores only 50 GB of data logs or the data logs for the last 24 hours. If the limit is exceeded, the DTS server automatically clears the cached logs.
      Warning If you clear the data logs of the source database during full data synchronization, the data synchronization task may fail. For example, full data synchronization takes more than 24 hours due to the large data volume in the source database and abnormal writing in the destination database. In this case, if the data logs of the source database are cleared during full data synchronization, DTS cannot obtain the data logs generated 24 hours ago. Therefore, the data synchronization task may fail.
Other limits
  • Requirements for the objects to be synchronized:
    • DTS supports schema synchronization for the following types of objects: database, schema, and table. \
    • DTS does not synchronize data of the following types: TIMESTAMP, CURSOR, ROWVERSION, HIERACHYID, SQL_VARIANT, SPATIAL GEOMETRY, SPATIAL GEOGRAPHY, and TABLE.
    • DTS does not synchronize tables that contain computed columns.
  • DDL operations cannot be synchronized. If you perform DDL operations in the source database during data synchronization, the data synchronization task fails. If you need to perform DDL operations, we recommend that you perform the operations in the destination database and then perform the operations in the source database.
  • To ensure that the latency of data synchronization is accurate, DTS adds a heartbeat table to the source database. The name of the heartbeat table is dts_log_heart_beat.
  • 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 full data synchronization, DTS uses read and write resources of the source and destination databases. This may increase the loads of 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 tablespace of the destination database is larger than that of the source database.
  • We recommend that you do not use gh-ost or pt-online-schema-change to perform data definition language (DDL) operations on source tables during data synchronization. Otherwise, data synchronization may fail.

Supported 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.

SQL operations that can be synchronized

Operation type SQL statements
DML INSERT, UPDATE, and DELETE

Procedure

  1. Log on to the DTS console.
  2. In the left-side navigation pane, click Data Synchronization.
  3. At the top of the Synchronization Tasks page, select the region where the destination instance resides.
    Select a region
  4. In the upper-right corner of the page, click New Console.
  5. On the Create Task page, configure the source and destination databases.
    Section Parameter Description
    N/A Task Name

    DTS automatically generates a task name. We recommend that you specify an informative name for easy identification. You do not need to use a unique task name.

    Source Database Database Type Select SQL Server.
    Access Method Select Alibaba Cloud Instance.
    Instance Region Select the region where the source ApsaraDB RDS for SQL Server instance resides.
    Instance ID Select the ID of the source ApsaraDB RDS for SQL Server instance.
    Database Account Enter the database account of the source ApsaraDB RDS for SQL Server instance. The account must have the owner permissions on the objects to be migrated. A privileged account has the required permissions.
    Database Password

    Enter the password of the database account.

    Destination Database Database Type Select MySQL.
    Access Method Select Alibaba Cloud Instance.
    Instance Region Select the region where the destination ApsaraDB RDS for MySQL instance resides.
    RDS Instance ID Select the ID of the destination ApsaraDB RDS for MySQL instance.
    Database Account Enter the database account of the destination ApsaraDB RDS for MySQL instance. The account must have the read and write permissions on the destination database.
    Database Password

    Enter the password of the database account.

    Encryption

    Select Non-encrypted or SSL-encrypted. If you want to select SSL-encrypted, you must enable SSL encryption for the ApsaraDB RDS for MySQL instance before you configure the data synchronization task. For more information, see Configure SSL encryption on an ApsaraDB RDS for MySQL instance.

  6. In the lower part of the page, click Test Connectivity and Proceed.
  7. Select objects for the task and configure advanced settings.
    • Basic Settings
      Parameter Description
      Task Stages

      By default, you must select both Schema Synchronization and Full Data Synchronization. After the precheck, DTS synchronizes the historical data of the selected objects from the source instance 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 identical table names, the precheck is passed. Otherwise, an error is returned during precheck and the data synchronization task cannot be started.
        Note You can use the object name mapping feature to rename the tables that are synchronized to the destination database. You can use this feature if the source and destination databases contain identical table names and the tables in the destination database cannot be deleted or renamed. For more information, see Rename an object to be synchronized.
      • 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 consistency is not guaranteed and your business may be exposed to potential risks.
        • If the source and destination databases have the same schema, DTS does not synchronize data records that have the same primary keys as data records in the destination database.
        • 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.
      Schema Mapping Mode of Source and Destination Databases
      Select a schema mapping mode based on your business requirements.
      Warning If you do not use the schema names of the source database, the source tables in different schemas must have unique names.
      SQL Server Incremental Synchronization Mode
      • Incremental Synchronization Based on Logs of Source Database:
        • Advantages:
          • Low latency and good performance
          • No intrusion to the source database
        • Disadvantages:
          • Heap tables and tables without primary keys are not supported.
          • DTS tasks may be interrupted due to large volumes of data written to the source database and frequent log truncation and archiving.
      • Incremental Synchronization Based on Logs of Source Database:
        • Advantages:
          • Heap tables and tables without primary keys are supported.
          • Log truncation in the source database does not interrupt DTS tasks.
        • Disadvantages:
          • DTS creates Change Data Capture (CDC) records in the source databases and tables.
          • The latency of this mode is higher than the log-based parsing mode.
      Select Objects

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

      Note You can select tables or databases as the objects to be synchronized.
      Rename Databases and Tables
      • 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 Rename an object to be synchronized.
      • To rename multiple objects at a time, click in the upper-right corner of the Selected Objects section. For more information, see Rename an object to be synchronized.
      Filter data

      You can specify WHERE conditions to filter data. For more information, see Use SQL conditions to filter data.

      Select the SQL operations to be synchronized In the Selected Objects section, right-click an object. In the dialog box that appears, select the DDL and DML operations that you want to synchronize. For more information, see SQL operations that can be synchronized.
    • Advanced Settings
      Parameter Description
      Set Alerts
      Specify whether to set alerts for the data synchronization task. If the task fails or the synchronization latency exceeds the threshold, the alert contacts will receive notifications.
      • Select No if you do not want to set alerts.
      • Select Yes to set alerts. In this case, you must also set the alert threshold and alert contacts.
      Capitalization of Object Names in Destination Instance

      Specify the capitalization of database names, table names, and column names in the destination instance. By default, DTS default policy is selected. You can select other options to make sure that the capitalization of object names is consistent with that of the source or destination database. For more information, see Specify the capitalization of object names in the destination instance.

      Retry Time for Failed Connections
      Specify the retry time for failed connections. Valid values: 10 to 1440. Unit: minutes. Default value: 120. We recommend that you set the retry time to more than 30 minutes. If DTS reconnects to the source and destination databases within the specified time, DTS resumes the data synchronization task. Otherwise, the data synchronization task fails.
      Note
      • If multiple DTS instances have the same source or destination database, the lowest value takes effect. For example, the retry time is set to 30 minutes for Instance A and 60 minutes for Instance B, DTS retries failed connections at an interval of 30 minutes.
      • When DTS retries a connection, you are charged for the DTS instance. We recommend that you specify the retry time based on your business needs. You can also release the DTS instance at your earliest opportunity after the source and destination instances are released.
  8. 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 task fails to pass the precheck, you can click the Info icon icon next to each failed item to view details.
      • You can troubleshoot the issues based on the causes and run a precheck again.
      • If you do not need to troubleshoot the issues, you can ignore failed items and run a precheck again.
  9. Wait until the Success Rate becomes 100%. Then, click Next: Purchase Instance.
  10. On the Purchase Instance page, specify the Billing Method and Instance Class parameters for the data synchronization instance. The following table describes the parameters.
    Section Parameter Description
    Parameters Billing Method
    • Subscription: You can pay for your subscription when you create an instance. We recommend that you select the subscription billing method for long-term use because it is more cost-effective than the pay-as-you-go billing method. You can save more costs with longer subscription periods.
    • Pay-as-you-go: A pay-as-you-go instance is billed on an hourly basis. We recommend that you select the pay-as-you-go billing method for short-term use. If you no longer require your pay-as-you-go instance, you can release it to reduce costs.
    Instance Class DTS provides several instance classes that have different performance in synchronization speed. You can select an instance class based on your business scenario. For more information, see Specifications of data synchronization channels.
    Subscription Length If you select the subscription billing method, set the subscription length and the number of instances that you want to create. The subscription length can be one to nine months or one to three years
    Note This parameter is available only if you select the subscription billing method.
  11. Read and select Data Transmission Service (Pay-as-you-go) Service Terms.
  12. Click Buy and Start to start the data synchronization task. You can view the progress of the task in the task list.