Data Transmission Service:Synchronize data from RDS for MySQL to a self-managed MySQL

Usage notes

• During initial full data synchronization, DTS consumes read and write resources from the source and destination databases, which increases the database load. If database performance is poor, instance specifications are low, or business traffic is heavy (for example, the source database has many slow SQL queries or tables without primary keys, or the destination database experiences deadlocks), the database load increases and may even cause the service to become unavailable. Before you synchronize data, evaluate the performance of your source and destination instances. We recommend performing data synchronization during off-peak hours, for example, when the CPU utilization of both instances is below 30%.

• During full data synchronization, concurrent writes can cause table fragmentation in the destination instance. As a result, the destination instance uses more table space than the source instance.

Billing

Limitations

If tables to be migrated in the source database have no primary key or unique constraint, and none of the fields are unique, the destination database may contain duplicate data.

• During data synchronization, do not use tools such as gh-ost or pt-online-schema-change to perform online DDL operations on the synchronization objects in the source database. Otherwise, the synchronization task fails.

• If a source table lacks a primary key or a unique constraint and contains non-unique data, duplicate data may be created in the destination database.

Supported synchronization topologies

• One-to-one one-way synchronization

• One-to-many one-way synchronization

• Cascading one-way synchronization

• Many-to-one one-way synchronization

For more information about each synchronization topology and its precautions, see Data synchronization topologies.

Supported SQL operations

Limitations

• Incompatible with triggers

  If you synchronize an entire database and a trigger within that database updates another table in the same database, data inconsistency may occur between the source and destination databases. For a solution, see Configure a data synchronization or migration task for a source database that contains a trigger.

• RENAME TABLE limitations

  The RENAME TABLE operation can cause data inconsistency. For example, if you select only Table A for synchronization and it is renamed to Table B in the source instance, Table B is not synchronized to the destination instance. To prevent this issue, select the entire database that contains both Table A and Table B as the synchronization object when you configure the data synchronization task.

Procedure

1. Purchase a data synchronization instance. For more information, see Purchase a DTS instance.
   Note When you purchase the instance, select MySQL for both the source and destination instances, and select One-way Synchronization for the synchronization topology.

2. Log on to the Data Transmission Service (DTS) console.

3. In the left-side navigation pane, click Data Synchronization.

4. At the top of the Data Synchronization page, select the region where the data synchronization instance resides.

5. Find the purchased data synchronization instance and click Configure Synchronization Task.

6. Configure the source and destination instances for the synchronization task.

   Category	Setting	Description
   N/A	Synchronization Task Name	DTS automatically generates a task name. For easier identification, we recommend specifying a descriptive name. The name does not need to be unique.
   Source Instance Information	Instance Type	Select RDS Instance.
   	Instance Region	The region where you purchased the data synchronization instance. This setting cannot be changed.
   	Instance ID	Select the ID of the source RDS instance.
   	Database Account	Enter the database account of the RDS instance. Note If the RDS instance runs MySQL 5.5 or MySQL 5.6, you do not need to configure Database Account and Database Password.
   	Database Password	Enter the password for the database account.
   	Connection Method	Select Non-encrypted or SSL-encrypted as required. If you select SSL-encrypted, you must first enable SSL encryption for the RDS instance. For more information, see Configure SSL encryption. Important Currently, the Encryption parameter is available only for regions in the Chinese mainland and the China (Hong Kong) region.
   Destination Instance Information	Instance Type	Select Self-managed Database with VPC Connection.
   	Instance Region	The region of the destination instance that you selected when you purchased the data synchronization instance. This setting cannot be changed.
   	Peer VPC	Select the ID of the VPC to which the self-managed database is connected.
   	Database Type	The value is fixed at MySQL and cannot be changed.
   	IP Address	Enter the IP address of the server on which the self-managed MySQL database is deployed.
   	Port	Enter the service port of the self-managed MySQL database. The default value is 3306.
   	Database Account	Enter the account for the self-managed MySQL database. Note The account must have the REPLICATION CLIENT, REPLICATION SLAVE, SHOW VIEW, and SELECT privileges on all synchronization objects.
   	Database Password	Enter the password for the database account.

7. In the lower-right corner of the page, click Set Whitelist and Next.

   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 IP address 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 self-managed database is hosted 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 IP address whitelist of the database to allow DTS to access the database. For more information, see Whitelist DTS server IP addresses.

   Warning

   Adding the public IP address blocks of the DTS service, either automatically or manually, may pose security risks. Using this product, you acknowledge that you understand and accept the potential security risks and that you must implement basic security measures. These measures include, but are not limited to, strengthening password security, limiting the ports open to each CIDR block, using authentication for internal API calls, and regularly checking and restricting unnecessary CIDR blocks. Alternatively, you can connect through a private network using a leased line, VPN Gateway, or Smart Access Gateway.

8. Configure the synchronization policy and objects.

   Parameter	Description
   Select Synchronization Objects	In the Source Objects box, select the objects to synchronize and click the icon to move them to the Selected Objects box. You can select objects at the database and table levels. Note If you select an entire database as a synchronization object, all schema change operations on objects within that database are synchronized to the destination database. By default, object names in the destination database are the same as in the source database. To rename an object in the destination database, use the object name mapping feature. For more information, see Set object names in the destination instance.
   Object Name Mapping	Change the names of synchronized objects in the destination instance. For more information, see Map databases, tables, and columns.
   Replicate temporary tables to the destination database during online DDL operations on source tables in DMS	If you use Data Management (DMS) to perform online DDL changes on the source database, you can choose whether to synchronize the temporary tables generated by the DDL changes. Yes: Synchronizes the temporary tables generated by online DDL changes. Note If a large amount of temporary table data is generated by online DDL changes, the data synchronization task may be delayed. No: Does not synchronize the temporary tables generated by online DDL changes. Only the original DDL operations from the source database are synchronized. Note This option causes tables in the destination database to be locked.
   Retry duration for connection failure to source or destination database	If DTS cannot connect to the source or destination instance, it retries for 720 minutes (12 hours) by default. You can also specify a custom retry duration. If DTS reconnects to the source or destination instance within the specified duration, the synchronization task automatically resumes. Otherwise, the task fails. Note You are billed for task run time during connection retries. Customize the retry duration based on your business needs, or release the DTS instance as soon as the source and destination instances are released.

9. After completing the preceding configurations, click Next in the lower-right corner of the page.

10. Configure advanced settings for initial synchronization.

    Note

    • This step initializes the schema and data of the selected objects from the source instance to the destination instance to establish a baseline for subsequent incremental data synchronization.

    • The initial synchronization types include initial schema synchronization and initial full data synchronization. By default, you must select both Initial Schema Synchronization and Initial Full Data Synchronization.

11. After completing the preceding configurations, click Precheck and Start in the lower-right corner of the page.

    Note

    • A precheck runs before the synchronization task starts, and you can only start the task after it passes.

    • If the precheck fails, click the icon next to the failed item to view the details.

      • You can fix the issues based on the cause and run the precheck again.

      • If you do not need to fix the items that triggered warnings, you can click Ignore or Ignore Warnings and Rerun Precheck to skip the warnings and run the precheck again.

12. After the Precheck dialog box shows Precheck Passed, close the Precheck dialog box. The synchronization task starts.

13. Wait for the task to complete link initialization and enter the Synchronizing state.

    You can view the status of the data synchronization task on the Data Synchronization page.

    The task list includes columns for Instance ID/Task Name, Status, Synchronization Overview (latency and speed), Billing Method, Synchronization Topology, and Actions. The Actions column provides options such as Suspend Synchronization, Change to Subscription, and Upgrade. At the top of the page, you can search for tasks by name and filter or sort them by status.