Synchronize data from an ApsaraDB RDS for MySQL 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 database load. 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 synchronizing data, you must evaluate 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 usage 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 objects during data synchronization. Otherwise, data synchronization may fail.
• If the disk space usage of 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 ensure that the destination cluster has sufficient storage space.

Supported source database types

You can use DTS to synchronize data from the following types of MySQL databases:

• ApsaraDB RDS for MySQL
• User-created database hosted on ECS
• User-created database connected over Express Connect, VPN Gateway, or Smart Access Gateway

SQL operations that can be synchronized

• DDL operations: CREATE TABLE, DROP TABLE, RENAME TABLE, TRUNCATE TABLE, ADD COLUMN, and DROP 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 initial schema synchronization.

Procedure

1. Purchase a data synchronization instance.
   Note On the buy page, set Source Instance to MySQL, 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	Select RDS Instance.
   	Instance Region	The region of the source instance. The region is the same as the source region that you selected when you purchased the data synchronization instance. You cannot change the value of this parameter.
   	Instance ID	Select the ID of the source RDS instance.
   	Database Account	Enter the database account of the source RDS instance. For more 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.
   	Database Password	Enter the password for the source database account.
   	Encryption	Select Non-encrypted or SSL-encrypted. If you want to select SSL-encrypted, you must enable SSL encryption for the RDS instance before you configure the data synchronization task. For more information, see Configure SSL encryption for an RDS for MySQL instance. Notice The Encryption parameter is available only for regions in mainland China and the Hong Kong (China) region.
   Destination Instance Details	Instance Type	The value of this parameter is set to AnalyticDB and cannot be changed.
   	Instance Region	The region of the destination instance. The region is the same as the destination region that you selected when you purchased the data synchronization instance. 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 AnalyticDB for MySQL cluster. For more information about the permissions that are required for the account, see Permissions required for database accounts.
   	Database Password	Enter the password for the destination database account.

7. In the lower-right corner of the page, click Set Whitelist and Next.
8. Configure the synchronization policy and objects.
   

   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 instance 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 change the names of the tables to be synchronized by using the object name mapping feature. You can use this feature if the source and destination databases contain identical table names and tables in the destination database cannot be deleted or renamed. For more information, see Specify the name of an object in the destination instance. 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 some 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 some 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. Note Only INSERT, UPDATE, DELETE, and ADD COLUMN operations can be synchronized.
   Objects to be synchronized	Select objects from the Available section and click the icon to move the objects to the Selected section. You can select tables and 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 ADD COLUMN operations on the table are synchronized to the destination database. After an object is synchronized to the destination database, the name of the object remains unchanged. You can change the names of the objects that are synchronized to the destination cluster by using the object name mapping feature. For more information about how to use this feature, see Specify the name of an object in the destination instance.

9. In the lower-right corner of the page, click Next.
10. Specify a type for the tables to be synchronized 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 to be synchronized 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, 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, click the icon next to each failed item to view details. Troubleshoot the issues based on the causes and run the precheck again.
12. Close the Precheck dialog box after the following message is displayed: The precheck is passed.
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 Data Synchronization page.

    

Troubleshoot the synchronization failure that occurs due to field type changes

In this example, the data of a table named customer fails to be synchronized to the destination AnalyticDB for MySQL cluster.

1. In the destination AnalyticDB for MySQL cluster, create a table named customer_new with the same schema as the customer table.
2. Run the INSERT INTO SELECT command to copy the data of the customer table and insert the data into the customer_new table. This ensures that the data of the two tables is consistent.
3. Rename or delete the customer table. Then, change the name of the customer_new table to customer.
4. Restart the data synchronization task in the DTS console.