This topic describes how to migrate incremental data from an Amazon RDS for PostgreSQL database to an ApsaraDB RDS for PostgreSQL database 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 database is 10.4-R1 to 11.4-R1.
  • The Public accessibility option of Amazon RDS for PostgreSQL is set to Yes. This ensures that DTS can access Amazon RDS for PostgreSQL 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 database.
  • An ApsaraDB RDS for PostgreSQL instance is created. For more information, see Create an RDS for PostgreSQL instance.
    Note
    • The version of the ApsaraDB RDS for PostgreSQL database 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 database is larger than the total size of the data in the Amazon RDS for PostgreSQL database.

Notes

  • 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%.
  • The objects to be migrated must have PRIMARY KEY or UNIQUE constraints and all fields must be unique. Otherwise, duplicate data may exist in the destination database and 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.
  • Only data manipulation language (DML) operations, such as INSERT, UPDATE, DELETE, and UPDATE operations, can be migrated.
  • During data migration, DTS creates a replication slot for the Amazon RDS for PostgreSQL database. The replication slot is prefixed with dts_sync_. DTS automatically clears historical replication slots every 90 minutes to prevent them from occupying disk space.
    Note If a migration task is released or fails, DTS automatically clears the replication slot. After a switchover between primary and secondary Amazon RDS for PostgreSQL databases, you must log on to the secondary database to manually clear the replication slot.
    Replication slot information
  • DTS automatically resumes a failed data migration task. Before switching your workloads to the destination instance, you must stop or release the data migration task. Otherwise, the data from the source database will overwrite the data in the destination instance 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

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

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

  • Incremental data migration

    After full data migration is complete, DTS synchronizes incremental data from the Amazon RDS for PostgreSQL database to the ApsaraDB RDS for PostgreSQL database. 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 database The usage permission for pg_catalog The SELECT permission for the objects to be migrated The rds_superuser permission
ApsaraDB RDS for PostgreSQL database The create and usage permissions for the objects to be migrated The owner permission for schemas The owner permission for schemas

Data migration process

To avoid 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 performing incremental data migration, do not perform DDL operations on the objects to be migrated in the Amazon RDS for PostgreSQL database. Otherwise, the objects may fail to be migrated.

Preparations

  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 rules
  5. On the Security Groups page, click the Inbound tab in the Security Group section. On the Inbound tab, click Edit, and add CIDR blocks of DTS servers to the Edit inbound rules dialog box that appears. The CIDR blocks of DTS servers vary with the region where the destination database resides. For more information about the CIDR blocks of DTS servers, see Add the CIDR blocks of DTS servers to the security settings of on-premises databases.
    AWS postgresql入站规则
    Note
    • You only need to add the CIDR blocks of DTS servers that are located in the same region as the destination database. For example, the source database is located in Singapore and the destination database is located in Hangzhou. You only need to add the CIDR blocks of DTS servers that are located in the China (Hangzhou) region.
    • You can add all the required CIDR blocks to the inbound rule at one time.

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 information about the source and destination databases for the data migration task.
    Configure the source and destination databases
    Section Parameter Description
    N/A Task Name DTS automatically generates a task name. We recommend that you use 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 the instance type is set to User-Created Database with Public IP Address, you do not need to specify the instance region.
    Database Type Select PostgreSQL.
    Hostname or IP Address Enter the endpoint that is used to connect to the Amazon RDS for PostgreSQL database.
    Note You can find the endpoint on the Basic information page of the source Amazon RDS for PostgreSQL instance.
    Endpoint
    Port Number Enter the service port number of the Amazon RDS for PostgreSQL database. The default port number is 5432.
    Database Name Enter the name of the source Amazon RDS for PostgreSQL database.
    Database Account Enter the account for the Amazon RDS for PostgreSQL database. For more information about permissions required for the account, see Permissions required for database accounts.
    Database Password Enter the password for the database account.
    Note After the source database information is specified, click Test Connectivity next to Database Password to verify whether the specified information is valid. If the specified information is valid, the Passed message appears. If the Failed message appears, click Check in the Failed message. Modify the source database information as prompted.
    Destination Database Instance Type Select RDS Instance.
    Instance Region Select the region where the destination ApsaraDB RDS for PostgreSQL instance resides.
    RDS Instance ID Select the ID of the destination ApsaraDB RDS for PostgreSQL instance.
    Database Name Enter the name of the destination ApsaraDB RDS for PostgreSQL database. The name can be different from the name of the source Amazon RDS for PostgreSQL database.
    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.
    Database Account Enter the database account for the destination ApsaraDB RDS for PostgreSQL instance. For more information about permissions required for the account, see Permissions required for database accounts.
    Database Password Enter the password for the database account.
    Note After the destination database information is specified, click Test Connectivity next to Database Password to verify whether the specified information is valid. If the specified information is valid, the Passed message appears. If the Failed message appears, click Check in the Failed message. Modify the destination database information as prompted.
  6. In the lower-right corner of the page, click Set Whitelist and Next.
    Note The CIDR blocks of DTS servers are automatically added to the whitelist of the destination ApsaraDB RDS for PostgreSQL instance. This ensures that DTS servers can connect to the destination ApsaraDB RDS for PostgreSQL instance.
  7. Select the migration types and objects to be migrated.
    Select the migration types and objects to be migrated
    Parameter Description
    Migration types Select Schema Migration, Full Data Migration, and Incremental Data Migration.
    Objects to be migrated

    Select objects from the Available section and click the Right arrow icon to add the objects to the Selected section.

    Note
    • You can select columns, tables, or schemas as the objects to be migrated.
    • After an object is migrated to the destination database, the name of the object remains unchanged. You can change the name of an object in the destination ApsaraDB RDS for PostgreSQL instance by using the object name mapping feature provided by DTS. For more information about the authorization methods, 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 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 migration task.
    Note The migration task does not automatically end. You must manually stop the migration task. Select an appropriate time to manually stop the migration task. For example, you can stop the migration 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 appears 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. After the status of incremental data migration changes to The migration task is not delayed, manually stop the migration task.Stop a task during incremental migration
  12. Switch your workloads to the ApsaraDB RDS for PostgreSQL instance.