Data Transmission Service:Synchronize data from a PolarDB for MySQL cluster 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 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 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 data definition language (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 that you want to synchronize. You must ensure 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.

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

For more information about how to create and authorize a database account, see Create a database account for a PolarDB for MySQL cluster and Create a database account for an AnalyticDB for MySQL cluster.

Data type mappings

For more information, see Data type mappings for schema synchronization.

Procedure

1. Purchase a data synchronization instance.
   Note On the buy page, set Source Instance to PolarDB, set Target Instance to AnalyticDB for MySQL, and set Synchronization Topology to One-Way Synchronization.
2. Log on to the DTS console.
3. In the left-side navigation pane, click Data Synchronization.
4. At the top of the Synchronization Tasks page, select the region where the destination instance resides.
5. Find the data synchronization instance and click Configure Synchronization Channel in the Actions column.
6. Configure the source and destination instances.
   

   Section	Parameter	Description
   N/A	Synchronization 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 Instance Details	Instance Type	This parameter is set to PolarDB Instance and cannot be changed.
   	Instance Region	The source region that you selected on the buy page. You cannot change the value of this parameter.
   	PolarDB Instance ID	Select the ID of the source PolarDB cluster.
   	Database Account	Enter the database account of the source PolarDB cluster. For information about the permissions that are required for the account, see Permissions required for database accounts.
   	Database Password	Enter the password of the database account.
   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	Select the ID of the destination AnalyticDB for MySQL cluster.
   	Database Account	Enter the database account of the destination AnalyticDB for MySQL cluster. For information about the permissions that are required for the account, see Permissions required for database accounts.
   	Database Password	Enter the password of the database account.

7. In the lower-right corner of the page, click Set Whitelist and Next.
   Note DTS adds the CIDR blocks of DTS servers to the whitelists of the PolarDB for MySQL cluster and the AnalyticDB for MySQL cluster. This ensures that DTS servers can connect to the source and destination clusters.
8. Select the synchronization policy and the objects to be synchronized.
   

   Parameter	Description
   Initial Synchronization	You must select both Initial Schema Synchronization and Initial Full Data Synchronization in most cases. After the precheck, DTS synchronizes the schemas and data of the required objects from the source cluster to the destination cluster. The schemas and data are the basis for subsequent incremental synchronization.
   Processing Mode In Existed Target Table	Pre-check and Intercept: 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: skips the precheck for identical table names in the source and destination databases. Warning If you select Ignore, 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, initial data synchronization may fail. In this case, only specific columns are synchronized or the data synchronization task fails.
   Merge Multi Tables	If you select Yes, DTS adds the __dts_data_source column to each table to record data sources. In this case, DDL operations cannot be synchronized. No is selected by default. In this case, DDL operations can be synchronized. Note You can merge the data source columns based on tasks rather than tables. To merge only the data source columns of specific tables, you can create two data synchronization tasks.
   Synchronization Type	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 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 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. After an object is synchronized to the destination cluster, 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 AnalyticDB for MySQL. 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, you can click the 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.
12. Close the Precheck dialog box after the following message is displayed: The precheck is passed. Then, the data synchronization task starts.
13. Wait until the initial synchronization is complete and the data synchronization task is in the Synchronizing state.
    You can view the status of the data synchronization task on the Synchronization Tasks page.