Data Transmission Service:Synchronize data between ApsaraDB RDS for MySQL instances that belong to different Alibaba Cloud accounts

Prerequisites

• An ApsaraDB RDS for MySQL instance is created. For more information, see Create an ApsaraDB RDS for MySQL instance..

• The database type of the source and destination instances is RDS MySQL.

• The source and destination ApsaraDB RDS for MySQL instances have internal endpoints.

Precautions

• DTS uses read and write resources of the source and destination RDS instances during initial full data synchronization. This may increase the loads of the RDS instances. If the instance performance is unfavorable, the specification is low, or the data volume is large, database services may become unavailable. For example, DTS occupies a large amount of read and write resources in the following cases: a large number of slow SQL queries are performed on the source RDS instance, the tables have no primary keys, or a deadlock occurs in the destination RDS instance. Before data synchronization, evaluate the impact of data synchronization on the performance of the source and destination RDS instances. We recommend that you synchronize data during off-peak hours. For example, you can synchronize data when the CPU utilization of the source and destination RDS instances is less than 30%.

• We recommend that you do not use gh-ost or pt-online-schema-change to perform DDL operations on objects during data synchronization. Otherwise, data synchronization may fail.

• The tables to be migrated in the source database must have PRIMARY KEY or UNIQUE constraints and all fields must be unique. Otherwise, the destination database may contain duplicate data records.

• During initial full data synchronization, concurrent INSERT operations cause fragmentation in the tables of the destination instance. After initial full data synchronization is complete, the size of used tablespace of the destination instance is larger than that of the source instance.

• If the destination database is an ApsaraDB RDS for MySQL instance that does not run MySQL 5.7 or 8.0, DTS creates the dtssyncwriter database account that has write permissions and is exclusive to DTS for the destination database.

Billing

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 synchronization topologies, see Synchronization topologies.

SQL operations that can be synchronized

Limits

• Incompatibility with triggers

  If you select a database as the object to synchronize and the database contains a trigger that updates a table, data inconsistency may occur. For more information about how to resolve this issue, see Configure a data synchronization task for a source database that contains a trigger.

• Limits on RENAME TABLE operations

  RENAME TABLE operations may cause data inconsistency between the source and destination databases. For example, if only Table A is selected as the object to synchronize and is renamed Table B, Table B cannot be synchronized to the destination database. To prevent this situation, you can select the entire database in which Table A is located as the object to synchronize when you configure the data synchronization task.

Preparations

Set the Alibaba Cloud account that owns the destination ApsaraDB RDS instance as a trusted account. This allows DTS to access the cloud resources of the Alibaba Cloud account that owns the source ApsaraDB RDS instance. For more information, see Configure RAM authorization for cross-account DTS tasks.

Procedure

1. Purchase a data synchronization instance by using the Alibaba Cloud account that owns the destination ApsaraDB RDS instance. For more information, see Purchase a data synchronization instance.

   Note

   Select MySQL for both the source and destination instances. Select One-way Synchronization as the synchronization topology.

2. Use the Alibaba Cloud account that owns the destination ApsaraDB RDS instance to log on to the DTS console by using the Alibaba Cloud account that owns the destination ApsaraDB RDS instance.

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

4. In the upper part of the Data Synchronization Tasks page, select the region in which the destination instance resides.

5. Find the data synchronization instance and click Configure Task in the Actions column.

6. Configure the source and destination instances.

   Section	Parameter	Description
   N/A	Synchronization Task Name	The task name that DTS automatically generates. We recommend that you specify a descriptive name that makes it easy to identify the task. You do not need to use a unique task name.
   Source Instance Details	Instance Type	Select RDS Instance.
   	Instance Region	The source region that you selected on the buy page. The value of this parameter cannot be changed.
   	Apsara Stack Tenant Account ID of RDS Instance	The ID of the Alibaba Cloud account that owns the source ApsaraDB RDS instance. Note Before you configure this parameter, click RDS Instances of Other Alibaba Cloud Accounts in the Source Instance Details section.
   	Role Name	The name of the RAM role that you configured earlier in Preparations.
   	RDS Instance ID	The ID of the source instance.
   Destination Instance Details	Instance Type	Select RDS Instance.
   	Instance Region	The destination region that you selected on the buy page. The value of this parameter cannot be changed.
   	Instance ID	The ID of the destination instance.
   	Database Account	The database account of the destination instance. Note If the database engine of the destination ApsaraDB RDS instance is MySQL 5.5 or MySQL 5.6, you do not need to configure the Database Account or Database Password parameter.
   	Database Password	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 instance before you configure the data synchronization task. For more information, see Configure SSL encryption for an ApsaraDB RDS for MySQL instance. Important The Encryption parameter is available only within regions in the Chinese mainland and the China (Hong Kong) region.

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

   Warning

   If 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.

8. Select the synchronization policy and the objects to be synchronized.

   Parameter/Section	Description
   Select Object to Be Synchronized	Select one or more objects from the Available section and click the icon to move the objects to the Selected section. You can select tables or databases as the objects to be synchronized. Note If you select a database as the object to synchronize, all schema changes in the database are synchronized to the destination database. By default, after an object is synchronized to the destination database, the name of the object remains unchanged. You can use the object name mapping feature to rename the objects that are synchronized to the destination database. For more information, see Rename an object to be synchronized.
   Rename Databases and Tables	You can use the object name mapping feature to rename the objects that are synchronized to the destination instance. For more information, see Object name mapping.
   Source table DMS_ONLINE_Do you want to copy the temporary table to the target database during DDL	If you use DMS to perform online DDL operations on the source database, you can specify whether to synchronize temporary tables generated by online DDL operations. Yes: DTS synchronizes the data of temporary tables generated by online DDL operations. Note If online DDL operations generate a large amount of data, the data synchronization task may be delayed. No: DTS does not synchronize the data of temporary tables generated by online DDL operations. Only the original DDL data of the source database is synchronized. Note If you select No, the tables in the destination database may be locked.
   Retry Time for Failed Connection	By default, if DTS fails to connect to the source or destination database, DTS retries within the next 720 minutes (12 hours). You can specify the retry time based on your needs. 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 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.

9. In the lower-right corner of the page, click Next.

10. Select the initial synchronization types.

    • During initial synchronization, DTS synchronizes the schema and data of required objects from the source instance to the destination instance. The schema and data are the basis for subsequent incremental synchronization.

    • Initial synchronization includes initial schema synchronization and initial full data synchronization. In most cases, you must select both Initial Schema Synchronization and Initial Full Data Synchronization.

11. In the lower-right corner of the page, click Precheck.

    Important

    • Before you can start the data synchronization task, a precheck is performed. 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 icon next to each failed item to view details.

      • After you troubleshoot the issues based on the causes, you can run a precheck again.

      • If you do not need to troubleshoot the issues, you can ignore failed items and run a precheck again.

12. Close the Precheck dialog box after the The precheck is passed. message is displayed in the Precheck dialog box. Then, the data synchronization task starts.

13. Wait until initial synchronization is complete and the data synchronization task enters the Synchronizing state.

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