This topic describes how to migrate data from a PolarDB for PostgreSQL cluster to an ApsaraDB RDS for PostgreSQL instance by using Data Transmission Service (DTS).

Prerequisites

  • The source PolarDB for PostgreSQL cluster is created. For more information, see Create a cluster.
  • The destination ApsaraDB RDS for PostgreSQL instance is created. For more information, see Create an ApsaraDB RDS for PostgreSQL instance.
  • The available storage space of the destination database is larger than the total size of the data in the source database.

Limits

Category Description
Limits on the source database
  • The tables to be migrated from the source PolarDB for PostgreSQL cluster must contain primary keys or UNIQUE NOT NULL indexes.
  • If one or more long-running transactions exist in the source database and incremental data is migrated in the data migration task, the write-ahead logging (WAL) logs generated before the long-running transactions in the source database are committed may be accumulated. As a result, the disk space of the source database may be insufficient.
Other limits
  • During full data migration, concurrent INSERT operations cause fragmentation in the tables of the destination database. After full data migration is complete, the tablespace of the destination database is larger than that of the source database.
  • DTS attempts to resume data migration tasks that failed within the last seven days. Before you switch workloads to the destination instance, stop or release the data migration task. You can also execute the REVOKE statement to revoke the write permissions from the accounts that are used by DTS to access the destination instance. Otherwise, the data in the source database overwrites the data in the destination instance after the data migration task is resumed.

Billing

Migration type Instance configuration fee Internet traffic fee
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 Billing overview.
Incremental data migration Charged. For more information, see Billing overview.

Migration types

  • Schema migration

    DTS migrates the schemas of required objects from the source database to the destination database.

  • Full data migration

    DTS migrates historical data of required objects from the source database to the destination database.

  • Incremental data migration

    After full data migration is complete, DTS migrates incremental data from the source database to the destination database. Incremental data migration allows you to ensure service continuity when you migrate data between self-managed databases.

SQL operations that can be incrementally migrated

Operation type SQL statement
DML INSERT, UPDATE, and DELETE

Permissions required for database accounts

Database Schema migration Full data migration Incremental data migration References
PolarDB for PostgreSQL Permissions of a privileged account Create a database account
ApsaraDB RDS for PostgreSQL CREATE and USAGE permissions on the objects to be migrated Permissions of the schema owner Permissions of the schema owner Create an account on an ApsaraDB RDS for PostgreSQL instance

Procedure

  1. Go to the Data Migration Tasks page.
    1. Log on to the Data Management (DMS) console.
    2. In the top navigation bar, click DTS.
    3. In the left-side navigation pane, choose DTS (DTS) > Data Migration.
    Note You can also configure the settings by using the new DTS console.
  2. From the drop-down list to the right of Data Migration Tasks, select the region in which your data migration instance resides.
    Note If you use the new DTS console, select the region in which your data migration instance resides in the upper-left corner.
  3. Click Create Task. On the page that appears, configure the source and destination databases.
    Section Parameter Description
    N/A Task Name

    The name of the task. 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 Database Type The type of the source database. Select PolarDB for PostgreSQL.
    Access Method The access method of the source database. Select Alibaba Cloud Instance.
    Instance Region The region in which the source PolarDB for PostgreSQL cluster resides.
    Replicate Data Across Alibaba Cloud Accounts Specifies whether to migrate data across Alibaba Cloud accounts. In this example, No is selected because data is migrated within the same Alibaba Cloud account.
    Instance ID The ID of the PolarDB for PostgreSQL cluster.
    Database Name The name of the source database in the PolarDB for PostgreSQL cluster.
    Database Account The database account of the PolarDB for PostgreSQL cluster.
    Database Password

    The password of the database account.

    Destination Database Database Type The type of the destination database. Select PostgreSQL.
    Access Method The access method of the destination database. Select Alibaba Cloud Instance.
    Instance Region The region in which the destination ApsaraDB RDS for PostgreSQL instance resides.
    Instance ID The ID of the destination ApsaraDB RDS for PostgreSQL instance.
    Database Name The name of the destination database in the ApsaraDB RDS for PostgreSQL instance.
    Database Account The database account of the destination ApsaraDB RDS for PostgreSQL instance.
    Database Password

    The password of the database account.

  4. In the lower part of the page, click Test Connectivity and Proceed.
    Warning
    • If the source or destination database is an Alibaba Cloud database instance, such as an ApsaraDB RDS for MySQL or ApsaraDB for MongoDB instance, DTS automatically adds the CIDR blocks of DTS servers to the whitelist of the instance. If the source or destination database is a self-managed database hosted on an Elastic Compute Service (ECS) instance, DTS automatically adds the CIDR blocks of DTS servers to the security group rules of the ECS instance. 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 that is deployed in a data center or provided by a third-party cloud service provider, you must manually add the CIDR blocks of DTS servers to the whitelist of the database to allow DTS to access the database.
    • If the CIDR blocks of DTS servers are automatically or manually added to the whitelist 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: enhancing the security of your username and password, limiting the ports that are exposed, authenticating API calls, regularly checking the whitelist or ECS security group rules and forbidding unauthorized CIDR blocks, or connecting the database to DTS by using Express Connect, VPN Gateway, or Smart Access Gateway.
    • After the DTS task is complete or released, we recommend that you manually detect and remove the added CIDR blocks from the whitelist or ECS security group rules.
  5. Select objects for the task and configure advanced settings.
    • Basic Settings
      Parameter Description
      Task Stages
      • 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.
      Note If Incremental Data Migration is not selected, we recommend that you do not write data to the source instance during data migration. This ensures data consistency between the source and destination instances.
      Processing Mode of Conflicting Tables
      • Precheck and Report Errors: 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 tables that have the same names, the precheck is passed. Otherwise, an error is returned during the precheck and the data migration task cannot be started.

        Note You can use the object name mapping feature to rename the tables that are migrated to the destination database. You can use this feature if the source and destination databases contain tables that have identical names and the tables in the destination database cannot be deleted or renamed. For more information, see Map object names .
      • Ignore Errors and Proceed: skips the precheck for identical table names in the source and destination databases.
        Warning If you select Ignore Errors and Proceed, data consistency is not ensured, and your business may be exposed to potential risks.
        • If the source and destination databases have the same schema, DTS does not migrate data records that have the same primary keys as data records in the destination database.
        • If the source and destination databases have different schemas, only specific columns are migrated or the data migration task fails.
      Capitalization of Object Names in Destination Instance

      The capitalization of database names, table names, and column names in the destination instance. By default, DTS default policy is selected. You can select other options to ensure that the capitalization of object names is consistent with that in the source or destination database. For more information,see Specify the capitalization of object names in the destination instance.

      Source Objects

      Select one or more objects from the Source Objects section and click the Rightwards arrow icon to move the objects to the Selected Objects section.

      Selected Objects
      • To rename an object that you want to migrate to the destination instance, right-click the object in the Selected Objects section. For more information, see Map the name of a single object.
      • To rename multiple objects at a time, click Batch Edit in the upper-right corner of the Selected Objects section. For more information, see Map multiple object names at a time.
      Note 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.
    • Advanced Settings
      Parameter Description
      Set Alerts
      Specifies whether to set alerts for the data migration task. If the task fails or the migration latency exceeds the threshold, the alert contacts will receive notifications. Valid values:
      • No: does not set alerts.
      • Yes: sets alerts. If you select Yes, you must also set the alert threshold and alert contacts.
      Retry Time for Failed Connections
      The retry time range for failed connections. Valid values: 10 to 1440. Unit: minutes. Default value: 120. We recommend that you set the parameter to a value greater than 30. 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
      • If you set different retry time ranges for multiple data migration tasks that have the same source or destination database, the value that is set later takes precedence.
      • When DTS retries a connection, you are charged for the data migration task. We recommend that you specify the retry time range based on your business requirements. You can also release the data migration task at the earliest opportunity after the source and destination databases are released.
      Configure ETL
      Specify whether to configure the extract, transform, and load (ETL) feature. For more information, see What is ETL?.
  6. Click Next: Save Task Settings and Precheck in the lower part of the page.
    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.
  7. Wait until the Success Rate becomes 100%. Then, click Next: Purchase Instance.
  8. On the Purchase Instance page, specify the Instance Class parameter for the data migration instance. The following table describes the parameter.
    Section Parameter Description
    Parameters Instance Class

    DTS provides several instance classes that have different performance in migration speed. You can select an instance class based on your business scenario. For more information, see Specifications of data migration instances.

  9. Read and select the check box for Data Transmission Service (Pay-as-you-go) Service Terms.
  10. Click Buy and Start to start the data migration task. You can view the progress of the task in the task list.