Synchronize data from a PolarDB for MySQL cluster to an AnalyticDB for PostgreSQL instance

Precautions

• DTS uses read and write resources of the source and destination databases during initial full data synchronization. This may increase the load of the database server. 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%.
• 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 tablespace of the destination instance is larger than that of the source cluster.

Limits

• You can select only tables as the objects to be synchronized.
• You cannot synchronize the following types of data: BIT, VARBIT, GEOMETRY, ARRAY, UUID, TSQUERY, TSVECTOR, and TXID_SNAPSHOT.
• Prefix indexes cannot be synchronized. If the source database contains prefix indexes, data may fail to be synchronized.
• We recommend that you do not use gh-ost or pt-online-schema-change to perform data definition language (DDL) operations on objects during data synchronization. Otherwise, data synchronization may fail.

SQL operations that can be synchronized

• Data manipulation language (DML) operations: INSERT, UPDATE, and DELETE
• DDL operations: ADD COLUMN and RENAME COLUMN
  Note The CREATE TABLE operation is not supported. To synchronize data from a new table, you must add the table to the selected objects. For more information, see Add an object to a data synchronization task.

Supported synchronization topologies

• One-way one-to-one synchronization
• One-way one-to-many synchronization
• One-way many-to-one synchronization

Term mappings

Procedure

1. Purchase a data synchronization instance. For more information, see Purchase procedure.
   Warning You cannot select PolarDB for MySQL cluster as the instance type. To synchronize data from a PolarDB for MySQL cluster, you can select User-Created Database Connected Over Express Connect, VPN Gateway, or Smart Access Gateway. On the buy page, set Source Instance to MySQL, set Target Instance to AnalyticDB for PostgreSQL, 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 User-Created Database Connected Over Express Connect, VPN Gateway, or Smart Access Gateway. Note You cannot select PolarDB for MySQL cluster as the instance type. To synchronize data from a PolarDB for MySQL cluster, you can select User-Created Database Connected Over Express Connect, VPN Gateway, or Smart Access Gateway.
   	Instance Region	The region of the PolarDB for MySQL cluster. The region is the same as the source region that you selected on the buy page. You cannot change the value of this parameter.
   	Peer VPC	Select the ID of the VPC where the PolarDB for MySQL cluster resides. To obtain the VPC ID, you can log on to the PolarDB console and click the cluster ID. In the Basic Information section of the Overview page, you can view the ID of the VPC where the cluster resides.
   	Database Type	The value of this parameter is set to MySQL and cannot be changed.
   	IP Address	Enter the private IP address of the PolarDB for MySQL cluster. You can obtain the private IP address by pinging the VPC-facing endpoint of the PolarDB for MySQL cluster.
   	Port Number	Enter the service port number of the PolarDB for MySQL cluster. The default port number is 3306.
   	Database Account	Enter the database account that is used to connect to the PolarDB for MySQL cluster. Note The database account must have the SELECT permission on the required objects, the REPLICATION CLIENT permission, the REPLICATION SLAVE permission, and the SHOW VIEW permission.
   	Database Password	Enter the password of the source database account.
   Destination Instance Details	Instance Type	The value of this parameter is set to AnalyticDB for PostgreSQL and cannot be changed.
   	Instance Region	The region of the destination instance. The region is the same as the destination region that you selected on the buy page. You cannot change the value of this parameter.
   	Instance ID	Select the ID of the instance.
   	Database Name	Enter the name of the destination database in the instance.
   	Database Account	Enter the of the instance. For more information, see Configure an account. Note You can also enter an account that has the RDS_SUPERUSER permission. For more information, see Manage users and permissions.
   	Database Password	Enter the password of the destination 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 instance. This ensures that DTS servers can connect to the source cluster and destination instance.
8. Select the synchronization policy and the objects to be synchronized.
   

   Setting	Parameter	Description
   Select the synchronization policy	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 instance. The schemas and data are the basis for subsequent incremental synchronization.
   	Processing Mode In Existed Target Table	Clear Target Table Skips the Schema Name Conflict item during the precheck. Clears the data in the destination table before initial full data synchronization. If you want to synchronize your business data after testing the data synchronization task, you can select this mode. Ignore Skips the Schema Name Conflict item during the precheck. Adds data to the existing data during initial full data synchronization. If you want to synchronize data from multiple tables to one table, you can select this mode.
   	Synchronization Type	Select the types of operations that you want to synchronize based on your business requirements. Insert Update Delete AlterTable
   Select the objects to be synchronized	N/A	Select tables from the Available section and click the icon to move the tables to the Selected section. Note You can select only tables as the objects to be synchronized. You can use the object name mapping feature to change the names of the columns that are synchronized to the destination database. For more information, see Specify the name of an object in the destination instance.

9. Specify the primary key column and distribution column of the table that you want to synchronize to the instance.
   

   Note The page in this step appears only if you select Initial Schema Synchronization. For more information about primary key columns and distribution columns, see Define constraints and Define table distribution.
10. 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 a precheck again.
11. Close the Precheck dialog box after the following message is displayed: The precheck is passed. Then, the data synchronization task starts.
12. 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.