This topic describes how to migrate incremental data from a self-managed 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 self-managed PostgreSQL database to Alibaba Cloud, you can select all of the supported migration types to ensure service continuity.

This topic uses a self-managed database with a public IP address as an example to describe how to configure an incremental data migration task. For information about how to perform full data migration, see Migrate full data from a self-managed PostgreSQL database to an ApsaraDB RDS for PostgreSQL instance.

Prerequisites

  • The self-managed database runs PostgreSQL 9.4.8 or a later version, PostgreSQL 9.5, PostgreSQL 9.6, or PostgreSQL10.0.
  • The available storage space of the ApsaraDB RDS for PostgreSQL instance is larger than the total size of the data in the self-managed PostgreSQL database.
  • The service port of the self-managed 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 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%.
  • If you select a schema as the object to be migrated and create a table in the schema or run the RENAME command to rename the table, you must run the ALTER TABLE schema.table REPLICA IDENTITY FULL; command before you write data to the table.
    Note Replace the schema and table in the preceding sample command with the actual schema name and table name.
  • The tables to be migrated in the source database must have PRIMARY KEY or UNIQUE constraints and all fields must be unique. Otherwise, the destination database may contain duplicate data records.
  • 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 database will overwrite the data in the destination instance after the task is resumed.

Limits

  • 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.
  • The name of the source database cannot contain hyphens (-), for example, dts-testdata.
  • If a primary/secondary switchover is performed on the source database during incremental data migration, DTS does not support resumable transmission.
  • Data may be inconsistent between the primary and secondary nodes of the source database due to synchronization delay. Therefore, you must use the primary node as the data source when you migrate data.
    Note We recommend that you migrate data during off-peak hours. You can modify the transfer rate of full data migration based on the read/write performance of the source database. For more information, see Modify the transfer rate of full data migration.
  • DTS does not check the validity of metadata such as sequences. You must manually check the validity of metadata.
  • After your workloads are switched to the destination database, newly written sequences do not increment from the maximum value of the sequences in the source database. Therefore, you must query the maximum value of the sequences in the source database before you switch your workloads to the destination database. Then, you must specify the queried maximum value as the starting value of the sequences in the destination database. You can execute the following statements to query the maximum value of the sequences in the source database:
    do language plpgsql $$
    declare
      nsp name;
      rel name;
      val int8;
    begin
      for nsp,rel in select nspname,relname from pg_class t2 , pg_namespace t3 where t2.relnamespace=t3.oid and t2.relkind='S'
      loop
        execute format($_$select last_value from %I.%I$_$, nsp, rel) into val;
        raise notice '%',
        format($_$select setval('%I.%I'::regclass, %s);$_$, nsp, rel, val+1);
      end loop;
    end;
    $$;
  • To ensure that the data migration task runs as expected, you can perform a primary/secondary switchover only on an ApsaraDB RDS for PostgreSQL instance V11. In this case, you must set the rds_failover_slot_mode parameter to sync. For more information, see Logical Replication Slot Failover.
    Warning If you perform a primary/secondary switchover on a self-managed PostgreSQL database or an ApsaraDB RDS for PostgreSQL instance of other versions, the data migration task stops.
  • During incremental data migration, DTS migrates only data manipulation language (DML) operations. DML operations include INSERT, DELETE, and UPDATE.
    Note Only data migration tasks that are created after October 1, 2020 can migrate data definition language (DDL) operations. To do this, you must create a trigger and function in the source database to obtain the DDL information before you configure the task. For more information, see Use triggers and functions to implement incremental DDL migration for PostgreSQL databases.

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.

Permissions required for database accounts

Database Schema migration Full data migration Incremental data migration
Self-managed PostgreSQL database The USAGE permission on pg_catalog The SELECT permission on the objects to be migrated The permissions of the superuser role
ApsaraDB RDS for PostgreSQL instance The CREATE and USAGE permissions on the objects to be migrated The permissions of the schema owner The permissions of the schema owner

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

Data migration process

The following table describes how DTS migrates the schemas and data of the source PostgreSQL database. The process prevents data migration failures that are caused by dependencies between objects.

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 DTS does not migrate plug-ins. In addition, DTS does not migrate functions that are written in the C programming language.
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. Incremental data migration allows you to ensure service continuity when you migrate data from a self-managed PostgreSQL database.
Note
  • During incremental data migration, DTS migrates only DML operations. DML operations include INSERT, DELETE, and UPDATE.
  • Incremental data migration does not support the BIT data type.

Before you begin

  1. Download the PostgreSQL source code from the official website, and compile and install the source code.
    1. Download the source code from the PostgreSQL official website based on the version of the self-managed PostgreSQL database.
    2. Run the ./configure, make, and make install commands to in sequence to configure, compile, and install the source code.
      Notice
      • When you compile and install PostgreSQL, the operating system version of PostgreSQL must be consistent with the GNU Compiler Collection (GCC) version.
      • If an error occurs when you run the ./configure command, you can adjust the command based on the error message. For example, if the error message is readline library not found. Use --without-readline to disable readline support., you can change the command to ./configure --without-readline.
      • If you use other methods to install PostgreSQL, you must compile the ali_decoding plug-in in a test environment that has the same OS version and GCC version.
  2. Download the ali_decoding plug-in provided by DTS, and compile and install the plug-in.
    1. Download ali_decoding.
    2. Copy the ali_decoding directory to the contrib directory of PostgreSQL (compiled and installed). contrib directory
    3. Go to the ali_decoding directory and replace the content of the Makefile file with the following script:
      # contrib/ali_decoding/Makefile
      MODULE_big = ali_decoding
      MODULES = ali_decoding
      OBJS    = ali_decoding.o
      
      DATA = ali_decoding--0.0.1.sql ali_decoding--unpackaged--0.0.1.sql
      
      EXTENSION = ali_decoding
      
      NAME = ali_decoding
      
      #subdir = contrib/ali_decoding
      #top_builddir = ../..
      #include $(top_builddir)/src/Makefile.global
      #include $(top_srcdir)/contrib/contrib-global.mk
      
      #PG_CONFIG = /usr/pgsql-9.6/bin/pg_config
      #pgsql_lib_dir := $(shell $(PG_CONFIG) --libdir)
      #PGXS := $(shell $(PG_CONFIG) --pgxs)
      #include $(PGXS)
      
      # Run the following commands to install the source code.
      ifdef USE_PGXS
      PG_CONFIG = pg_config
      PGXS := $(shell $(PG_CONFIG) --pgxs)
      include $(PGXS)
      else
      subdir = contrib/ali_decoding
      top_builddir = ../..
      include $(top_builddir)/src/Makefile.global
      include $(top_srcdir)/contrib/contrib-global.mk
      endif
    4. Go to the ali_decoding directory, run the make and make install commands in sequence to compile ali_decoding and obtain the files required to install ali_decoding.
    5. Copy the following files to the specified location. Specify location
  3. Create a database and schema in the destination ApsaraDB RDS for PostgreSQL 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 on an ApsaraDB RDS for PostgreSQL instance and Appendix: User and schema management.

Procedure

  1. Log on to the DTS console.
  2. In the left-side navigation pane, click Data Migration.
  3. In the upper part of the Migration Tasks page, select the region where the RDS instance resides.
  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 to identify the task. You do not need to specify a unique task name.
    Source Database Instance Type Select an instance type based on the deployment of the source database. In this example, select User-Created Database with Public IP Address.
    Note If you select other instance types, you must deploy the network environment for the self-managed database. For more information, see Preparation overview.
    Instance Region If you select User-Created Database with Public IP Address as the instance type, you do not need to configure the Instance Region parameter.
    Note If a whitelist is configured for the self-managed PostgreSQL database, you must add the CIDR blocks of DTS servers to the whitelist of the 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 self-managed PostgreSQL database. In this example, enter the public IP address.
    Port Number Enter the service port number of the self-managed PostgreSQL database. The default port number is 5432.
    Database Name Enter the name of the self-managed PostgreSQL database.
    Database Account Enter the account that is used to log on to the self-managed PostgreSQL database. 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 information about the self-managed Oracle database, you can click Test Connectivity next to Database Password to check whether the information is valid. If the information is valid, the Passed message appears. If the Failed message appears, click Check next to Failed. Then, modify the information 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 name of the destination database in the RDS instance. The name can be different from the name of the self-managed PostgreSQL database.
    Note Before you configure the data migration task, you must create a database and schema in the destination RDS instance. For more information, see Before you begin.
    Database Account Enter the username of the account that is used to log on to the 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 of the database account.
    Note After you specify the information about the RDS instance, you can click Test Connectivity next to Database Password to check whether the information is valid. If the information is valid, the Passed message appears. If the Failed message appears, click Check next to Failed. Then, modify the information based on the check results.
  6. In the lower-right corner of the page, click Set Whitelist and Next.
  7. Select the migration types and the objects that you want to migrate. Select the migration types and the objects that you want to migrate
    Setting Description
    Select the 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. In this example, select all of the three migration types.
    Note If Incremental Data Migration is not selected, do not write data to the self-managed PostgreSQL database during full data migration. This ensures data consistency between the self-managed database and the RDS instance.
    Select the objects that you want to migrate

    Select one or more objects from the Available section and click the Rightwards arrow icon to move 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 RDS instance, the name of the object remains the same as that in the self-managed PostgreSQL database. You can use the object name mapping feature to rename the objects that are migrated to the destination RDS 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 RDS instance. For more information, see Object name mapping.
    Specify the retry time range 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 following 12 hours. You can specify the retry time range based on your business requirements. If DTS reconnects to the self-managed database or RDS instance within the specified period of 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 range based on your business requirements. You can also release the DTS instance at your earliest opportunity after the source and destination instances are released.
  8. Click Precheck.
    Note
    • A precheck is performed before the migration task starts. The migration task only starts after the precheck succeeds.
    • If the precheck fails, click the Note icon next to each failed check item to view the related details. Fix the issues as instructed and run the precheck again.
  9. After the data migration task passes the precheck, click Next.
  10. In the Confirm Settings dialog box, configure the Channel Specification parameter. Then, read and select Data Transmission Service (Pay-as-you-go) Service Terms.
  11. Click Buy and Start to start the data migration task.
    • Full data migration

      Do not manually stop a full data migration task. If you manually stop a full data migration task, the data that is migrated to the RDS instance may be incomplete. You can wait until the full data migration task automatically stops.

    • Incremental data migration

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

      Note We recommend that you manually stop an incremental data migration task at an appropriate point in time. For example, you can stop the task during off-peak hours or before you switch your workloads over to the RDS instance.
      1. Wait until Incremental Data Migration and The data migration task is not delayed appear in the progress bar of the data migration task. Then, stop writing data to the self-managed Oracle 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 data migration task is not delayed again. Then, manually stop the migration task. The data migration task is not delayed
  12. Switch your workloads to the destination RDS instance.

What to do next

The database accounts that are used for data migration have the read and write permissions. After data migration is completed, you must delete the accounts of both the self-managed PostgreSQL database and the ApsaraDB RDS for PostgreSQL instance to ensure security.