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

Prerequisites

The tables to be migrated contain primary keys or UNIQUE NOT NULL indexes.

Precautions

  • DTS uses read and write resources of the source and destination databases during full data migration. 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 you migrate data, evaluate 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 usage of the source and destination databases is less than 30%.
  • 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.
  • To ensure that the delay time 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.Schema of a heartbeat table
  • DTS automatically resumes a failed data migration task. Before you switch your workloads to the destination database, stop or release the data migration task. Otherwise, the data from the source database will overwrite the data in the destination database after the task is resumed.

Billing

Migration type Instance configurations Internet traffic
Schema migration and full data migration Free of charge. Charged only when data is migrated from Alibaba Cloud over the Internet. For more information, see Pricing.
Incremental data migration Charged. For more information, see Pricing.

Migration types

Migration type Description
Schema migration DTS migrates the schemas of the required objects to the destination PolarDB cluster. DTS supports schema migration for the following types of objects: table, view, synonym, trigger, stored procedure, function, package, and user-defined type.
Notice However, if an object contains triggers, data will become inconsistent between the source and destination databases.
Full data migration DTS migrates historical data of the required objects from the source PolarDB cluster to the destination PolarDB cluster.
Notice 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 migration DTS retrieves redo log files from the source PolarDB cluster. Then, DTS synchronizes incremental data from the source PolarDB cluster to the destination PolarDB cluster. The following SQL operations can be synchronized:
  • INSERT, UPDATE, and DELETE operations
  • CREATE TABLE operations
    Notice The CREATE TABLE operations used to create partition tables or tables that contain functions cannot be synchronized.
  • ALTER TABLE, DROP TABLE, RENAME TABLE, CREATE INDEX, and ADD INDEX operations

Incremental data migration allows you to ensure service continuity when you migrate data between PolarDB clusters.

Preparation

Set the value of the wal_level parameter to logical for the source PolarDB cluster. This setting ensures that logical decoding is supported in write-ahead logging (WAL). For more information, see Configure cluster parameters.

Warning If you change the value of the wal_level parameter, the source PolarDB cluster is restarted. Perform this operation with caution.

Procedure

  1. Log on to the DTS console.
  2. In the left-side navigation pane, click Data Migration.
  3. At the top of Migration Tasks the page, select the region where the destination cluster resides.
    Select a region
  4. In the upper-right corner of the page, click Create Migration Task.
  5. Configure the source and destination databases.
    Migrate data between PolarDB clusters compatible with Oracle
    Section Parameter Description
    N/A 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 Database Instance Type Select PolarDB.
    Instance Region Select the region where the source PolarDB cluster resides.
    PolarDB Instance ID Select the ID of the source PolarDB cluster.
    Database Name Enter the name of the source database.
    Database Account Enter the privileged account of the source PolarDB cluster. For more information, see Create a database account.
    Database Password Enter the password of the source database account.
    Note After you specify the source database parameters, click Test Connectivity next to Database Password to verify whether the specified parameters are valid. If the specified parameters are valid, the Passed message appears. If the Failed message appears, click Check next to Failed. Modify the source database parameters based on the check results.
    Destination Database Instance Type Select PolarDB.
    Instance Region Select the region where the destination PolarDB cluster resides.
    PolarDB Instance ID Select the ID of the destination PolarDB cluster.
    Database Name Enter the name of the destination database.
    Database Account Enter the database account of the destination PolarDB cluster. The account must have the owner permission on the database.
    Notice You can specify the database owner when you create a database.
    Database Password Enter the password of the destination database account.
    Note After you specify the destination database parameters, click Test Connectivity next to Database Password to verify whether the parameters are valid. If the specified parameters are valid, the Passed message appears. If the Failed message appears, click Check next to Failed. Modify the destination database parameters based on the check results.
  6. In the lower-right corner of the page, click Set Whitelist and Next.
    DTS adds the CIDR blocks of DTS servers to the whitelists of the source and destination PolarDB clusters. This ensures that DTS servers can connect to the source and destination PolarDB clusters.
  7. Select the migration types and objects to be migrated.
    Select the migration types and objects to be migrated
    Parameter Description
    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, 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.
    Objects Select objects from the Available section and click the Right arrow icon to move the objects to the Selected section. You can select columns, tables, or schemas as the objects to be migrated.
    Notice
    • After an object is migrated to the destination database, the name of the object remains unchanged. You can change the names of the objects that are migrated to the destination PolarDB cluster by using the object name mapping feature. For more information about how to use this feature, see Object name mapping.
    • If you use the object name mapping feature on an object, other objects that are dependent on the object may fail to be migrated.
  8. Click Precheck on the lower right of the page.
    Note
    • A precheck is performed for a data migration task. A data migration task can be started only if it passes the precheck.
    • If the precheck fails, click Note icon corresponding to each failed item to view the details. Fix the problems as instructed and run the precheck again.
  9. After the precheck is passed, click Next.
  10. On the Confirm Settings dialog box that appears, specify Channel Specification and select the 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

      Do not manually stop a migration task. Otherwise, data migrated to the destination database will be incomplete. Wait until the data migration task stops when it is complete.

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

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

      Note Select an appropriate time point to manually end the migration task. For example, you can end the migration task during off-peak hours or before you switch your workloads to the destination cluster.
      1. When the task progress bar switches to Incremental Data Migration and the message The migration task is not delayed appears, stop writing new data to the source database for a few minutes. Then, the progress bar will show the latency of the incremental data migration.
      2. When the status of incremental data migration changes to The migration task is not delayed, manually stop the migration task.Stop the incremental migration task

Related topics

Switch workloads to the destination database