This topic describes how to migrate incremental data from an Amazon RDS for PostgreSQL instance to an ApsaraDB RDS for PostgreSQL instance by using Data Transmission Service (DTS). DTS supports schema migration, full data migration, and incremental data migration. You can select all of the supported migration types to ensure service continuity.

Prerequisites

  • The version of the Amazon RDS for PostgreSQL instance is 10.4 to 12.
  • The Public accessibility option of the Amazon RDS for PostgreSQL instance is set to Yes. This ensures that DTS can access the instance over the Internet.
  • The value of the rds.logical_replication parameter is set to 1. This ensures that DTS can read incremental data from the Amazon RDS for PostgreSQL instance.
  • An ApsaraDB RDS for PostgreSQL instance is created. For more information, see Create an ApsaraDB RDS for PostgreSQL instance.
    Note
    • The version of the ApsaraDB RDS for PostgreSQL instance is 10 or 11. To migrate data between different database versions, create a pay-as-you-go instance to verify compatibility.
    • The available storage space of the ApsaraDB RDS for PostgreSQL instance must be larger than the total size of the data in the Amazon RDS for PostgreSQL instance.

Precautions

  • 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 objects to be migrated must have PRIMARY KEY or UNIQUE constraints and all fields must be unique. Otherwise, the destination database may contain duplicate data records and data migration may fail.
  • 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.
  • In this scenario, DTS can migrate only data manipulation language (DML) operations, such as INSERT, DELETE, and UPDATE.
  • During data migration, DTS creates a replication slot for the Amazon RDS for PostgreSQL instance. The replication slot is prefixed with dts_sync_. DTS automatically clears historical replication slots every 90 minutes to reduce storage usage.
    Note If the data migration task is released or fails, DTS automatically clears the replication slot. If a primary/secondary switchover is performed on the Amazon RDS for PostgreSQL instance, you must log on to the secondary database to clear the replication slot.
    Replication slot information
  • If a data migration task fails, DTS automatically resumes the task. Before you switch your workloads to the destination instance, stop or release the data migration task. Otherwise, the data in the source instance will overwrite the data in the destination instance after the task is resumed.

Billing

Migration type Task 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 Pricing.
Incremental data migration Charged. For more information, see Pricing.

Migration types

  • Schema migration
    DTS migrates the schemas of the required objects to the ApsaraDB RDS for PostgreSQL instance. DTS supports schema migration for the following types of objects: table, trigger, view, sequence, function, user-defined type, rule, domain, operation, and aggregate.
    Note DTS does not migrate functions that are written in the C programming language.
  • Full data migration

    DTS migrates historical data of the required objects from the Amazon RDS for PostgreSQL instance to the ApsaraDB RDS for PostgreSQL instance.

  • Incremental data migration

    After full data migration is complete, DTS synchronizes incremental data from the Amazon RDS for PostgreSQL instance to the ApsaraDB RDS for PostgreSQL instance. Incremental data migration allows you to ensure service continuity when you migrate data between PostgreSQL databases.

Permissions required for database accounts

Database Schema migration Full data migration Incremental data migration
Amazon RDS for PostgreSQL The USAGE permission on pg_catalog The SELECT permission on the objects to be migrated The rds_superuser permission
ApsaraDB RDS for PostgreSQL The CREATE and USAGE permissions on the objects to be migrated The permissions of the schema owner The permissions of the schema owner

Data migration process

To prevent data migration failures caused by dependencies between objects, DTS migrates the schemas and data of the source PostgreSQL database in the following order:

  1. Migrate the schemas of tables, views, sequences, functions, user-defined types, rules, domains, operations, and aggregates.
  2. Perform full data migration.
  3. Migrate the schemas of triggers and foreign keys.
  4. Perform incremental data migration.
    Note Before incremental data migration, do not perform data definition language (DDL) operations on the objects in the Amazon RDS for PostgreSQL instance. Otherwise, the objects may fail to be migrated.

Before you begin

  1. Log on to the Amazon RDS Management Console.
  2. In the upper-right corner of the page, select the region where the destination instance resides.
  3. In the left-side navigation pane, click Databases. On the page that appears, click the ID of the destination database. The Basic Information page appears.
    Click the ID of the destination database
  4. In the Security group rules section, click the name of the security group corresponding to the existing inbound rule.
    Security group rule
  5. On the Security Groups page, click the Inbound tab in the Security Group section. On the Inbound tab, click Edit to add the CIDR blocks of DTS servers in the corresponding region to the inbound rule. For more information, see Add the CIDR blocks of DTS servers to the security settings of on-premises databases.
    Edit the inbound rule of the Amazon RDS for PostgreSQL instance
    Note
    • You need to add only the CIDR blocks of DTS servers that reside in the same region as the destination database. For example, the source database resides in the Singapore (Singapore) region and the destination database resides in the China (Hangzhou) region. You need to add only the CIDR blocks of DTS servers that reside in the China (Hangzhou) region.
    • You can add all of the required CIDR blocks to the inbound rule at a time.

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.
    Select a region
  4. In the upper-right corner of the page, click Create Migration Task.
  5. Configure the source and destination databases.
    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 for easy identification. You do not need to use a unique task name.
    Source Database Instance Type Select User-Created Database with Public IP Address.
    Instance Region Select the region where the source instance resides. If you select User-Created Database with Public IP Address as the instance type, you do not need to specify the Instance Region parameter.
    Database Type Select PostgreSQL.
    Hostname or IP Address Enter the endpoint that is used to access the Amazon RDS for PostgreSQL instance.
    Note You can obtain the endpoint on the Basic Information page of the Amazon RDS for PostgreSQL instance.
    Endpoint
    Port Number Enter the service port number of the Amazon RDS for PostgreSQL instance. The default port number is 5432.
    Database Name Enter the name of the source database in the Amazon RDS for PostgreSQL instance.
    Database Account Enter the database account of the Amazon RDS for PostgreSQL instance. For information about the permissions that are required for the account, see Permissions required for database accounts.
    Database Password Enter the password of the 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 RDS Instance.
    Instance Region Select the region where the ApsaraDB RDS for PostgreSQL instance resides.
    RDS Instance ID Select the ID of the ApsaraDB RDS for PostgreSQL instance.
    Database Name Enter the name of the destination database in the ApsaraDB RDS for PostgreSQL instance. The name can be different from the name of the source database in the Amazon RDS for PostgreSQL instance.
    Note Before you configure the data migration task, you must create a database in the ApsaraDB RDS for PostgreSQL instance. For more information, see Create a database on an ApsaraDB RDS for PostgreSQL instance.
    Database Account Enter the database account of the ApsaraDB RDS for PostgreSQL instance. For information about the permissions that are required for the account, see Permissions required for database accounts.
    Database Password Enter the password of the database account.
    Note After you specify the destination 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 destination database parameters based on the check results.
  6. In the lower-right corner of the page, click Set Whitelist and Next.
    Note DTS adds the CIDR blocks of DTS servers to the whitelist of the ApsaraDB RDS for PostgreSQL instance. This ensures that DTS servers can connect to the ApsaraDB RDS for PostgreSQL instance.
  7. Select the migration types and the objects to be migrated.
    Select the migration types and the objects to be migrated
    Setting Description
    Select the migration types Select Schema Migration, Full Data Migration, and Incremental Data Migration.
    Select the objects to be migrated

    Select one or more objects from the Available section and click the Rightwards arrow icon to add the objects to the Selected section.

    Note
    • You can select columns, tables, or schemas as the objects to be migrated.
    • By default, after an object is migrated to the destination instance, the name of the object remains unchanged. You can use the object name mapping feature to rename the objects that are migrated to the ApsaraDB RDS for PostgreSQL instance. 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 instance. For more information, see Object name mapping.
    Specify the retry time 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 next 12 hours. You can specify the retry time based on your needs. If DTS reconnects to the source and destination databases within the specified time, 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 based on your business needs. You can also release the DTS instance at your 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, 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 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.
    Note A task does not automatically stop during incremental data migration. You must manually stop the task. 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 instance.
    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. Stop a task during incremental data migration
  12. Switch your workloads to the ApsaraDB RDS for PostgreSQL instance.