Data Transmission Service:Migrate data from an ApsaraDB RDS for PPAS instance to a PolarDB for Oracle cluster

Prerequisites

• A PolarDB for Oracle cluster is created. For more information, see Create a cluster.
• The available storage space of the PolarDB for Oracle cluster is larger than the total size of the data in the ApsaraDB RDS for PPAS instance.
• If one or more uppercase letters exist in the names of the source database, tables, and fields in the ApsaraDB RDS for PPAS instance, you must enclose the names of the source database, tables, and fields in the PolarDB for Oracle cluster with double quotation marks (") when you create the objects in the cluster.
• To migrate incremental data from an ApsaraDB RDS for PPAS instance, you must submit a ticket to grant the permissions of the superuser role to the database account.

Limits

• DTS uses read and write resources of the source and destination databases during full data migration. 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 migrate data, evaluate the impact of data migration on the performance of the source and destination databases. We recommend that you migrate data during off-peak hours. For example, you can migrate data when the CPU utilization of the source and destination databases is less than 30%.
• 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.
• A single data migration task can migrate data from only one database. To migrate data from multiple databases, you must create a data migration task for each database.
• If a data migration task fails, DTS automatically resumes the task. Before you switch your workloads to the destination cluster, stop or release the data migration task. Otherwise, the data in the source database overwrites the data in the destination cluster after the task is resumed.
• After your workloads are switched to the destination database, newly written sequences do not increment from the maximum value of the sequences in the source database. Therefore, you must query the maximum value of the sequences in the source database before you switch your workloads to the destination database. Then, you must specify the queried maximum value as the starting value of the sequences in the destination database. You can execute the following statements to query the maximum value of the sequences in the source database:

  do language plpgsql $$
  declare
    nsp name;
    rel name;
    val int8;
  begin
    for nsp,rel in select nspname,relname from pg_class t2 , pg_namespace t3 where t2.relnamespace=t3.oid and t2.relkind='S'
    loop
      execute format($_$select last_value from %I.%I$_$, nsp, rel) into val;
      raise notice '%',
      format($_$select setval('%I.%I'::regclass, %s);$_$, nsp, rel, val+1);
    end loop;
  end;
  $$;

• When you migrate data from your ApsaraDB RDS for PPAS instance to a PolarDB for Oracle cluster, take note of the following items:
  • Make sure that the specifications of the PolarDB for Oracle cluster are higher than or equal to those of the ApsaraDB RDS for PPAS instance. Otherwise, slow SQL queries or out of memory (OOM) errors may occur because of insufficient CPU or memory resources after you migrate the data to the PolarDB for Oracle cluster. For more information about the recommended specifications of PolarDB for Oracle clusters, see Mapping between specifications of ApsaraDB RDS for PPAS instances and recommended specifications of PolarDB for Oracle clusters.
  • If you have special requirements for the number of connections and IOPS after migration, select appropriate specifications based on your business requirements. For more information, see Specifications of compute nodes.
  • If you use a cluster endpoint to connect your application to a PolarDB for Oracle cluster, read/write splitting is enabled. Then, the system forwards read requests to read-only PolarDB for Oracle nodes. This reduces the load on the PolarDB for Oracle cluster. For more information about how to obtain a cluster endpoint, see View or apply for an endpoint.

Mapping between specifications of ApsaraDB RDS for PPAS instances and recommended specifications of PolarDB for Oracle clusters

Make sure that the specifications of the PolarDB for Oracle cluster are higher than or equal to the specifications of your ApsaraDB RDS for PPAS instance. Otherwise, slow SQL queries or OOM errors may occur because of insufficient CPU or memory resources after you migrate the data to the PolarDB for Oracle cluster. The following table lists the recommended specifications of PolarDB for Oracle clusters.

Migration types

Billing

Permissions required for database accounts

Log on to the source Oracle database, create an account for data collection, and grant permissions to the account.

To create a database account and grant permissions to the database account, perform the following operations:

To create a database account in a PolarDB for Oracle cluster, follow the instructions in Create database accounts.

Procedure

1. Log on to the DTS console.
2. In the left-side navigation pane, click Data Migration.
3. At the top of the Migration Tasks page, select the region where the destination cluster resides.
4. In the upper-right corner of the page, click Create Migration Task.
5. Configure the source and destination databases.

   Section	Parameter	Description
   N/A	Task Name	DTS automatically generates a task name. We recommend that you specify an informative name to identify the task. You do not need to specify a unique task name.
   Source Database	Instance Type	Select User-Created Database Connected Over Express Connect, VPN Gateway, or Smart Access Gateway. You cannot select ApsaraDB RDS for PPAS as the instance type.
   	Instance Region	Select the region in which the ApsaraDB RDS for PPAS instance resides.
   	Peer VPC	Select the ID of the virtual private cloud (VPC) that is connected to the source database in the ApsaraDB RDS for PPAS instance.
   	Database Type	Select PPAS.
   	Version	Select the database engine version of the ApsaraDB RDS for PPAS instance.
   	IP Address	Enter the private IP address of the ApsaraDB RDS for PPAS instance.
   	Port Number	Enter the service port number of the ApsaraDB RDS for PPAS instance. The default port number is 3433.
   	Database Name	Enter the name of the source database in the ApsaraDB RDS for PPAS instance.
   	Database Account	Enter the username of the database account that is used to connect to the source database in the ApsaraDB RDS for PPAS instance. For information about the permissions that are required for the database account, see Permissions required for database accounts.
   	Database Password	Enter the password of the database account. Note After you specify the information about the self-managed Oracle database, you can click Test Connectivity next to Database Password to check whether the information is valid. If the information is valid, the Passed message appears. If the Failed message appears, click Check next to Failed. Then, modify the information based on the check results.
   Destination Database	Instance Type	Select PolarDB.
   	Instance Region	Select the region in which the destination PolarDB for Oracle cluster resides.
   	PolarDB Instance ID	Select the ID of the source PolarDB for Oracle cluster.
   	Database Name	The name of the destination database.
   	Database Account	Enter the username of the database account that is used to connect to the destination database in the PolarDB for Oracle cluster. For information about the permissions that are required for the database account, see Permissions required for database accounts.
   	Database Password	Enter the password of the database account. Note After you specify the information about the RDS instance, you can click Test Connectivity next to Database Password to check whether the information is valid. If the information is valid, the Passed message appears. If the Failed message appears, click Check next to Failed. Then, modify the information based on the check results.

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

   • If the source or destination database instance is an Alibaba Cloud database instance, such as an ApsaraDB RDS for MySQL or ApsaraDB for MongoDB instance, or is a self-managed database hosted on Elastic Compute Service (ECS), DTS automatically adds the CIDR blocks of DTS servers to the whitelist of the database instance or ECS security group rules. For more information, see Add the CIDR blocks of DTS servers to the security settings of on-premises databases. If the source or destination database is a self-managed database on data centers or is from other cloud service providers, you must manually add the CIDR blocks of DTS servers to allow DTS to access the database.
   • If the CIDR blocks of DTS servers are automatically or manually added to the whitelist of the database instance or ECS security group rules, security risks may arise. Therefore, before you use DTS to migrate data, you must understand and acknowledge the potential risks and take preventive measures, including but not limited to the following measures: enhance the security of your account and password, limit the ports that are exposed, authenticate API calls, regularly check the whitelist or ECS security group rules and forbid unauthorized CIDR blocks, or connect the database to DTS by using Express Connect, VPN Gateway, or Smart Access Gateway.
   • After the DTS task is completed or released, we recommend that you manually detect and remove the added CIDR blocks from the whitelist of the database instance or ECS security group rules.
7. Select the migration types and the objects to be migrated.
   

   Setting	Description
   Select the migration types	To perform only full data migration, select Schema Migration and Full Data Migration. To ensure service continuity during data migration, select Schema Migration, Full Data Migration, and Incremental Data Migration. Notice If Incremental Data Migration is not selected, we recommend that you do not write data to the source database during full data migration. This ensures data consistency between the source and destination databases. During schema migration and full data migration, do not perform DDL operations on the objects to be migrated. Otherwise, the objects may fail to be migrated.
   Select the objects to be migrated	Select one or more objects from the Available section and click the icon to move the objects to the Selected section. Note You can select columns, tables, or databases as the objects to be migrated. By default, after an object is migrated 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 migrated to the destination database. For more information, see Object name mapping. If you use the object name mapping feature to rename an object, other objects that are dependent on the object may fail to be migrated.
   Specify whether to rename objects	You can use the object name mapping feature to rename the objects that are migrated to the destination database. For more information, see Object name mapping.
   Specify the retry time range for failed connections to the source or destination database	By default, if DTS fails to connect to the source or destination database, DTS retries within the following 12 hours. You can specify the retry time range based on your business requirements. If DTS is reconnected to the source and the destination databases within the specified time range, DTS resumes the data migration task. Otherwise, the data migration task fails. Note When DTS retries a connection, you are charged for the DTS instance. We recommend that you specify the retry time range based on your business requirements. You can also release the DTS instance at your earliest opportunity after the source instance and destination cluster are released.

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

   • Before you can start the data migration task, a precheck is performed. You can start the data migration 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.
9. After the task passes the precheck, click Next.
10. In the Confirm Settings dialog box, specify the Channel Specification parameter and select Data Transmission Service (Pay-As-You-Go) Service Terms.
11. Click Buy and Start to start the data migration task.
    • Schema migration and full data migration

      We recommend that you do not manually stop the task during full data migration. Otherwise, the data migrated to the destination database will be incomplete. You can wait until the data migration task automatically stops.

    • Schema migration, full data migration, and incremental data migration

      The task does not automatically stop during incremental data migration. You must manually stop the task.

      Notice We recommend that you select an appropriate time to manually stop the data migration task. For example, you can stop the task during off-peak hours or before you switch your workloads to the destination cluster.
      1. Wait until Incremental Data Migration and The migration task is not delayed appear in the progress bar of the migration task. Then, stop writing data to the source database for a few minutes. The delay time of incremental data migration may be displayed in the progress bar.
      2. Wait until the status of incremental data migration changes to The migration task is not delayed again. Then, manually stop the migration task.