Data Transmission Service:Synchronize data from an ApsaraDB RDS instance to an AnalyticDB for MySQL cluster

Precautions

• DTS uses read and write resources of the source and destination databases during initial full data synchronization. This may increase the loads of the database servers. If the database performance or specifications are unfavorable, 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 database, the tables have no primary keys, or a deadlock occurs in the destination 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. For example, you can synchronize data when the CPU utilization of the source and destination databases is less than 30%.
• We recommend that you do not use gh-ost or pt-online-schema-change to perform DDL operations on the required objects during data synchronization. Otherwise, data may fail to be synchronized.
• Due to the limits of AnalyticDB for MySQL, if the disk space usage of the nodes in an AnalyticDB for MySQL cluster reaches 80%, the cluster is locked. We recommend that you estimate the required disk space based on the objects to be synchronized. You must make sure that the destination cluster has sufficient storage space.
• Prefix indexes cannot be synchronized. If the source database contains prefix indexes, data may fail to be synchronized.

Billing

SQL operations that can be synchronized

• DDL operations: CREATE TABLE, DROP TABLE, RENAME TABLE, TRUNCATE TABLE, ADD COLUMN, DROP COLUMN, and MODIFY COLUMN
• DML operations: INSERT, UPDATE, and DELETE

Permissions required for database accounts

Data type mappings

The data types of ApsaraDB RDS for MySQL and AnalyticDB for MySQL do not have one-to-one correspondence. During initial schema synchronization, DTS converts the data types of the source database into those of the destination database. For more information, see Data type mappings for schema synchronization.

Procedure

1. Purchase a data synchronization instance. For more information, see Purchase a DTS instance.
   Note On the buy page, set Source Instance to MySQL, Destination Instance to AnalyticDB MySQL, and Synchronization Topology to One-way Synchronization.
2. Go to the DTS console.
3. In the left-side navigation pane, click Data Synchronization.
4. In the upper part of the Data Synchronization Tasks page, select the region where the data synchronization instance resides.
5. Find the data synchronization instance and click Configure Task in the Actions column.
6. Configure the source instance and the destination cluster.
   

   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. You cannot change the value of this parameter.
   	Instance ID	The ID of the source ApsaraDB RDS instance.
   	Database Account	The database account of the source ApsaraDB RDS instance. For information about the permissions that are required for the account, see Permissions required for database accounts. Note If the database engine of the source 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	Specifies whether to encrypt the connection to the destination instance. 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.
   Destination Instance Details	Instance Type	This parameter is set to AnalyticDB and cannot be changed.
   	Instance Region	The destination region that you selected on the buy page. You cannot change the value of this parameter.
   	Version	Select 3.0.
   	Database	The ID of the destination AnalyticDB for MySQL cluster.
   	Database Account	The database account of the AnalyticDB for MySQL cluster. For information about the permissions that are required for the account, see Permissions required for database accounts.
   	Database Password	The password of the database account.

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

   • You do not need to modify the security settings for ApsaraDB instances (such as ApsaraDB RDS for MySQL and ApsaraDB for MongoDB) and ECS-hosted databases. DTS automatically adds the CIDR blocks of DTS servers to the whitelists of ApsaraDB instances or the security group rules of Elastic Compute Service (ECS) instances. For more information, see Add the CIDR blocks of DTS servers to the security settings of on-premises databases.
   • After data synchronization is complete, we recommend that you remove the CIDR blocks of DTS servers from the whitelists or security groups.
8. Select the synchronization policy and the objects to be synchronized.
   

   Parameter or setting	Description
   Select the initial synchronization types	You must select both Initial Schema Synchronization and Initial Full Data Synchronization in most cases. After the precheck is complete, DTS synchronizes the schema and data of required objects from the source instance to the destination cluster. The schema and data are the basis for subsequent incremental synchronization.
   Processing Mode In Existed Target Table	Precheck and Report Errors: checks whether the source and destination databases contain tables that share the same names. If the destination database does not contain tables that have the same names as those in the source database, 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. If the source and destination databases contain identical table names and the tables in the destination database cannot be deleted or renamed, you can use this feature. 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 inconsistency may occur 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, initial data migration may fail. In this case, only specific columns are migrated, or the data migration task fails.
   Merge Multi Tables	If you select Yes, DTS adds the __dts_data_source column to each table to store data sources. In this case, DDL operations cannot be synchronized. No is selected by default. In this case, DDL operations can be synchronized. Note If you set this parameter to Yes, all of the selected source tables in the task are merged into a destination table. If you want to merge only part of the source tables, you can create two data synchronization tasks.
   Select the operation types to be synchronized	Select the types of operations that you want to synchronize based on your business requirements. All operation types are selected by default. For more information, see SQL operations that can be synchronized.
   Select the objects to be synchronized	Select one or more objects from the Available section and click the icon to add 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 be synchronized, all schema changes in the database are synchronized to the destination database. If you select a table as the object to be synchronized, only the ADD COLUMN operations that are performed on the table 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 cluster. 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.
   Replicate Temporary Tables When DMS Performs DDL Operations	If you use Data Management (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 Connections	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. Specify a type for the tables that you want to synchronize to the destination database.
    

    Note After you select Initial Schema Synchronization, you must specify the type, primary key column, and partition key column for the tables that you want to synchronize to the destination AnalyticDB for MySQL cluster. For more information, see CREATE TABLE.
11. In the lower-right corner of the page, click Precheck.
    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, click the icon next to each failed item to view details.
      • After you troubleshoot the issues based on the causes, run a precheck again.
      • If you do not need to troubleshoot the issues, ignore failed items and run a precheck again.
12. Close the Precheck dialog box after the following message is displayed: Precheck Passed. 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 Synchronization Tasks page.

    

Troubleshoot the synchronization failure that occurs due to field type changes

If the data type of a field in the source table is changed during data synchronization, an error message is reported and the data synchronization task is interrupted. You can troubleshoot the issue by using the following method.

1. Create a table in the destination cluster based on the schema of source table that fails to be synchronized. For example, if a table named customer (Table A) fails to be synchronized, you can create a table named customer_new (Table B) in the destination cluster. Make sure that Table B has the same schema as Table A.
2. Run the INSERT INTO SELECT command to copy the data of Table A and insert the data into Table B. This ensures that the data of the two tables is consistent.
3. Rename or delete Table A. Then, change the name of Table B to customer.
4. Restart the data synchronization task in the DTS console.