This topic describes how to migrate incremental data from a user-created PostgreSQL database to an ApsaraDB RDS for PostgreSQL instance by using Data Transmission Service (DTS). DTS supports schema migration, full data migration, and incremental data migration. When you migrate data from a user-created PostgreSQL database to Alibaba Cloud, you can select all of the supported migration types to ensure service continuity.

This topic uses User-Created Database with Public IP Address as an example to describe how to configure an incremental data migration task. For information about how to perform only full data migration, see Migrate full data from a user-created PostgreSQL database to an ApsaraDB RDS for PostgreSQL instance.

Prerequisites

  • The version of the user-created PostgreSQL database is 9.4, 9.5, 9.6, or 10.0.
  • The available storage space of the ApsaraDB RDS for PostgreSQL instance is larger than the total size of the data in the user-created PostgreSQL database.
  • The service port of the user-created PostgreSQL database is accessible over the Internet.

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%.
  • The source database must have PRIMARY KEY or UNIQUE constraints and all fields must be unique. Otherwise, duplicate data may exist in the destination database.
  • 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.
  • During incremental data migration, only data manipulation language (DML) operations, such as INSERT, UPDATE, DELETE, and UPDATE operations, can be migrated.
  • DTS automatically resumes a failed data migration task. Before you switch your workloads to the destination instance, stop or release the data migration task. Otherwise, the data in 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.

Permissions required for database accounts

Database Schema migration Full data migration Incremental data migration
User-created PostgreSQL database The usage permission on pg_catalog The SELECT permission on the objects to be migrated The superuser permission
ApsaraDB RDS for PostgreSQL instance The create and usage permissions on the objects to be migrated The owner permission on schemas The owner permission on schemas

For more information about how to create and authorize a database account, see the following topics:

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:

Note For more information about schema migration, full data migration, and incremental data migration, see Terms.
Data migration process Description
1. Schema migration DTS migrates the schemas of tables, views, sequences, functions, user-defined types, rules, domains, operations, and aggregates to the destination database.
Note Functions that are written in the C programming language cannot be migrated.
2. Full data migration DTS migrates historical data of the required objects to the destination database.
3. Schema migration DTS migrates the schemas of triggers and foreign keys to the destination database.
4. Incremental data migration DTS migrates incremental data of the required objects to the destination database.
Note Incremental data migration does not support the bit data type.

Preparation 1: Install the logical flow replication plug-in and modify system settings

Before you configure an incremental data migration task, you must install the logical flow replication plug-in provided by DTS in the user-created PostgreSQL database.
Note In the following procedure, PostgreSQL 9.6 is used as an example.
  1. On the server of the user-created PostgreSQL database, run the wget command to download the logical flow replication plug-in based on the database version. Download the plug-in from one of the following links:
  2. Extract the plug-in from the compressed file.
    tar xvf tar xvf ali_decoding_9.6.tar
  3. Copy the ali_decoding.so file to the lib directory where PostgreSQL is installed.
    cp ali_decoding.so /usr/lib/postgresql/9.6/lib/
  4. Copy the ali_decoding.control file to the extension directory where PostgreSQL is installed.
    cp ali_decoding.control /usr/share/postgresql/9.6/extension/
  5. Log on to the user-created PostgreSQL database by using an account that has the superuser permission.
  6. Set the value of the max_replication_slots parameter to an integer greater than 1. In this example, set the value to 5.
    Note For more information, see PostgreSQL official documentation.
    ALTER SYSTEM set max_replication_slots = '5';
  7. Set the value of the wal_level parameter to logical.
    ALTER SYSTEM SET wal_level = logical;
  8. Set the value of the max_wal_senders parameter to an integer greater than 1. In this example, set the value to 5.
    Note The max_wal_senders parameter specifies the maximum number of concurrent tasks. We recommend that you set the value of this parameter to the same as the value of the max_replication_slots parameter.
    ALTER SYSTEM SET max_wal_senders = '5';
  9. Return to the shell of the server for the user-created PostgreSQL database and run the following command to restart the PostgreSQL service.
    service postgresql restart
  10. Log on to the user-created PostgreSQL database again and run the following command to check whether the replication slot can be created:
    SELECT * FROM pg_create_logical_replication_slot('replication_slot_test', 'ali_decoding');
    The following message indicates that the logical flow replication plug-in is installed.Check whether the plug-in is installed
  11. Add the CIDR blocks of DTS servers to the PostgreSQL configuration file (pg_hba.conf). For more information about how to edit this configuration file, see The pg_deploy.conf file. Skip this step if you have set the IP address in the pg_hba.conf file to 0.0.0.0/0.
    Note You only need to add the CIDR blocks of DTS servers that reside in the same region as the destination database. For more information, see Add the CIDR blocks of DTS servers to the security settings of on-premises databases.

Preparation 2: Create a database and schema in the destination RDS instance

Create a database and schema in the destination RDS instance based on the database and schema information of the objects to be migrated. The schema name of the source and destination databases must be the same. For more information, see Create a database and Schema management.

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 RDS instance resides.Select a region
  4. In the upper-right corner of the page, click Create Migration Task.
  5. Configure 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 specify an informative name for easy identification. You do not need to use a unique task name.
    Source Database Instance Type Select an instance type based on where the source database is deployed. The procedure in this topic uses User-Created Database with Public IP Address as an example.
    Note If you select other instance types, you must prepare the environments that are required for the source database. For more information, see Preparation overview.
    Instance Region If the instance type is set to User-Created Database with Public IP Address, you do not need to specify the instance region.
    Note If a whitelist is configured for the user-created PostgreSQL database, you must add the CIDR blocks of DTS servers to the whitelist of the user-created PostgreSQL database. You can click Get IP Address Segment of DTS next to Instance Region to obtain the CIDR blocks of DTS servers.
    Database Type Select PostgreSQL.
    Hostname or IP Address Enter the endpoint that is used to connect to the user-created PostgreSQL database. In this example, enter the public IP address.
    Port Number Enter the service port number of the user-created PostgreSQL database. The default port number is 5432.
    Database Name Enter the name of the user-created PostgreSQL database.
    Database Account Enter the account of the user-created PostgreSQL database. For more information about the permissions that are required for the account, see Permissions required for database accounts.
    Database Password Enter the password for 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 RDS Instance.
    Instance Region Select the region where the destination RDS instance resides.
    RDS Instance ID Select the ID of the destination RDS instance.
    Database Name Enter the database name of the destination RDS instance. The name can be different from the name of the user-created PostgreSQL database.
    Note Before you configure the data migration task, create a database and schema in the destination RDS instance. For more information, see Preparation 2: Create a database and schema in the destination RDS instance.
    Database Account Enter the database account of the destination RDS instance. For more information about the permissions that are required for the account, see Permissions required for database accounts.
    Database Password Enter the password for 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.
    Note The CIDR blocks of DTS servers are automatically added to the whitelist of the destination RDS instance. This ensures that DTS servers can connect to the destination RDS instance.
  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 migrate data with minimal downtime, select Schema Migration, Full Data Migration, and Incremental Data Migration. In this example, all of the three migration types are selected.
    Note If Incremental Data Migration is not selected, do not write data into the source database during full data migration. This ensures data consistency between the source and destination databases.
    Objects

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

    Note
    • You can select columns, tables, or Schemas as the objects to be migrated. You can select a Schema as an object to be migrated, and then create a new table in the source PostgreSQL database during data migration. In this case, you must run the following statement on the new table:
      ALTER TABLE schema.table REPLICA IDENTITY FULL;

      Replace the schema and table in the preceding sample statement with the actual schema name and table name.

    • After an object is migrated to the destination RDS instance, the name of the object remains the same as that in the user-created PostgreSQL database. You can change the names of the objects that are migrated to the destination RDS instance 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. 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, click the Info icon icon next to each failed item to view details. Troubleshoot the issues based on the causes and run the precheck again.
  9. After the task passes the precheck, click Next.
  10. In the Confirm Settings dialog box, specify the Channel Specification and select the Data Transmission Service (Pay-As-You-Go) Service Terms.
  11. Click Buy and Start to start the migration task.
    • Full data migration

      Do not manually stop a task during full data migration. Otherwise, data migrated to the destination database will be incomplete. Wait until the migration task automatically stops.

    • Incremental data migration

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

      Note 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 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. After the status of incremental data migration changes to The migration task is not delayed, manually stop the migration task.The migration task is not delayed
  12. Switch your workloads to the RDS instance.

What to do next

The database accounts used for data migration have the read/write permissions. After the data migration is complete, you must delete the accounts of both the user-created PostgreSQL database and the ApsaraDB RDS for PostgreSQL instance to ensure database security.