PolarDB is a next-generation relational database service that is developed by Alibaba Cloud. It is compatible with MySQL, PostgreSQL, and Oracle database engines. PolarDB provides superior computing and storage performance to meet the diverse requirements of your enterprise. This topic describes how to migrate data between PolarDB for Oracle clusters by using Data Transmission Service (DTS).

Prerequisites

  • The source and destination PolarDB for Oracle clusters reside in the China (Shanghai) region. This is because data migration between PolarDB for Oracle clusters is available only in the China (Shanghai) region.
  • The tables to be migrated from the source PolarDB for Oracle cluster contain primary keys or UNIQUE NOT NULL indexes.
  • The value of the wal_level parameter is set to logical for the source PolarDB for Oracle cluster. This setting ensures that logical encoding is supported in write-ahead logging (WAL). For more information, see Configure cluster parameters.

Usage notes

  • 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%.
  • A data migration task can migrate data from only a single database. To migrate data from multiple databases, you must create a data migration task for each database.
  • If you select a schema as the object to be migrated and create a table in the schema or execute the RENAME statement to rename the table during incremental data migration, you must execute the ALTER TABLE schema.table REPLICA IDENTITY FULL; statement before you write data to the table.
    Note Replace the schema and table variables in the preceding statement with your schema name and table name.
  • To ensure that the latency of incremental data migration is accurate, DTS adds a heartbeat table named dts_postgres_heartbeat to the source database. The following figure shows the schema of the heartbeat table. Table schema
  • If a data migration task fails, DTS automatically resumes the task. Before you switch your workloads to the destination database, stop or release the data migration task. Otherwise, the data in the source database overwrites the data in the destination database after the task is resumed.
  • If the source database has a long-running transaction and an incremental data migration task is in progress, the WAL logs that record the long-running transaction cannot be cleared and large storage space is occupied.

Billing

Migration typeTask configuration feeInternet traffic fee
Schema migration and full data migrationFree of charge. Charged only when data is migrated from Alibaba Cloud over the Internet. For more information, see Billing overview.
Incremental data migrationCharged. For more information, see Billing overview.

Migration types

Migration typeDescription
Schema migrationDTS migrates the schemas of the required objects from the source database to the destination PolarDB cluster. DTS supports schema migration for the following types of objects: table, view, synonym, stored procedure, stored function, package, and user-defined type.
Important DTS does not support triggers. If an object contains triggers, data inconsistency between the source and destination databases may occur.
Full data migrationDTS migrates the historical data of the required objects from the source database to the destination PolarDB cluster.
Important 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.
Incremental data migrationDTS retrieves redo log files from the source database. Then, DTS migrates incremental data from the source database to the destination PolarDB cluster. DTS can synchronize DML operations, such as INSERT, UPDATE, and DELETE. DTS cannot synchronize DDL operations.

Incremental data migration allows you to ensure service continuity when you perform data migration.

Procedure

  1. Log on to the DTS console.
    Note If you are redirected to the Data Management (DMS) console, you can click the old icon in the lower-right corner to go to the previous version of 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.
    Migrate data between PolarDB for Oracle clusters
    SectionParameterDescription
    N/ATask NameThe 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 specify a unique task name.
    Source DatabaseInstance TypeSelect PolarDB.
    Instance RegionThe region in which the source PolarDB cluster resides.
    PolarDB Instance IDThe ID of the source PolarDB for Oracle cluster.
    Database NameThe name of the source database.
    Database AccountA privileged account of the source PolarDB cluster. For more information, see Create database accounts.
    Database PasswordThe 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 DatabaseInstance TypeSelect PolarDB.
    Instance RegionThe region in which the destination PolarDB cluster resides.
    PolarDB Instance IDThe ID of the destination PolarDB for Oracle cluster.
    Database NameThe name of the destination database.
    Database AccountThe database account of the destination PolarDB for Oracle cluster. The account must have the permissions of the database owner.
    Important You can specify the database owner when you create a database.
    Database PasswordThe password of the database account.
    Note After you specify the information about the destination 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.
  6. In the lower-right corner of the page, click Set Whitelist and Next.
    Warning If the CIDR blocks of DTS servers are automatically or manually added to the whitelist of the database or instance, or to the 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 username 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.
  7. Select the migration types and objects to be migrated.
    Select the migration types and the objects to be migrated
    SettingDescription
    Select 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.
    Important
    • If Incremental Data Migration is not selected, we recommend that you do not write data to the source database during schema migration or 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 migratedSelect one or more objects from the Source Objects section and click the Rightwards arrow icon to add the objects to the Selected Objects section. You can select columns, tables, or schemas as the objects to be migrated.
    Important
    • 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 PolarDB cluster. 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 objectsYou can use the object name mapping feature to rename the objects that are migrated to the destination cluster. For more information, see Object name mapping.
    Specify the retry time range for failed connections to the source or destination databaseBy 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 range based on your needs. If DTS reconnects to the source and 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 the earliest opportunity after the source and destination instances are released.
  8. In the lower-right corner of the page, click Precheck.
    Note
    • Before you can start the data migration task, DTS performs a precheck. 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 Info icon 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 may be incomplete. You can wait until the data migration task automatically stops.

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

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

      Important 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 latency 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. Stop an incremental data migration task

References

Switch workloads to the destination database