This topic describes how to migrate 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.

Prerequisites

  • A self-managed PostgreSQL database and an ApsaraDB RDS for PostgreSQL instance are created. For information about how to create the destination ApsaraDB RDS for PostgreSQL instance, see Create an ApsaraDB RDS for PostgreSQL instance. For information about the supported versions, see Overview of data migration scenarios.
    Note For compatibility purposes, we recommend that the source ApsaraDB RDS for PostgreSQL instance runs a database engine version that is earlier than or the same as the database engine version that is run on the destination ApsaraDB RDS for PostgreSQL instance.

    If the source ApsaraDB RDS for PostgreSQL instance runs a later database engine version than the destination ApsaraDB RDS for PostgreSQL instance, compatibility issues may occur.

  • The available storage space of the destination ApsaraDB RDS for PostgreSQL instance is larger than the total size of the data in the self-managed PostgreSQL database.

Limits

Category Description
Limits on the source database
  • The server to which the source database belongs must have sufficient outbound bandwidth. Otherwise, the data migration speed decreases.
  • The tables to migrate must have PRIMARY KEY or UNIQUE constraints and all fields must be unique. Otherwise, the destination database may contain duplicate data records.

    The name of the source database cannot contain hyphens (-). Example: dts-testdata.

  • If you select tables as objects to migrate and you need to edit tables (such as renaming tables or columns) in the destination database, up to 1,000 tables can be migrated in a single data migration task. If you run a task to migrate more than 1,000 tables, a request error occurs. In this case, we recommend that you split the tables and configure multiple tasks to migrate the tables, or configure a task to migrate the entire database.
  • If you need to migrate incremental data, you must make sure that the following requirements are met:
    • The value of the wal_level parameter must be set to logical.

    • For an incremental data migration, the WAL logs of the source database must be stored for more than 24 hours. For a full data and incremental data migration, the WAL logs of the source database must be stored for at least seven days. After full data migration is complete, you can set the retention period to more than 24 hours. Otherwise, DTS may fail to obtain the WAL logs and the task may fail. In exceptional circumstances, data inconsistency or loss may occur. Make sure that you set the retention period of WAL logs in accordance with the preceding requirements. Otherwise, the Service Level Agreement (SLA) of DTS does not ensure service reliability or performance.

  • Limits on operations:
    • If you perform a primary/secondary switchover on the self-managed PostgreSQL database, the data migration task fails.
    • During schema migration and full data migration, do not perform DDL operations to change the schemas of databases or tables. Otherwise, the data migration task fails.
Other limits
  • Data may be inconsistent between the primary and secondary nodes of the source database due to migration latency. Therefore, you must use the primary node as the data source when you migrate data.
  • A data migration task can migrate data from only a single database. To migrate data from multiple databases, you must create a data migration task for each database.
  • During incremental data migration, if you select a schema as the object to migrate, take note of the following limits: If you create a table in the schema or execute the RENAME statement to rename the table, you must execute the ALTER TABLE schema.table REPLICA IDENTITY FULL; statement before you write data to the table.
    Note Replace the schema and table in the preceding sample statement with your actual schema name and table name.
  • 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 $$
declare
  nsp name;
  rel name;
  val int8;
begin
  for nsp,rel in select nspname,relname from pg_class t2 , pg_namespace t3 where t2.relnamespace=t3.oid and t2.relkind='S'
  loop
    execute format($_$select last_value from %I.%I$_$, nsp, rel) into val;
    raise notice '%',
    format($_$select setval('%I.%I'::regclass, %s);$_$, nsp, rel, val+1);
  end loop;
end;
$$;
  • DTS creates the following temporary tables in the source database to obtain the DDL statements of incremental data, the schemas of incremental tables, and the heartbeat information. During data migration, do not delete temporary tables in the source database. Otherwise, the data migration task may fail. After the DTS instance is released, temporary tables are automatically deleted.

    public.DTS_PG_CLASS, public.DTS_PG_ATTRIBUTE, public.DTS_PG_TYPE, public.DTS_PG_ENUM, public.DTS_POSTGRES_HEARTBEAT, public.DTS_DDL_COMMAND, and public.DTS_ARGS_SESSION.

  • To ensure that the latency of incremental data migration is accurate, DTS creates a heartbeat table named dts_postgres_heartbeat in the source database.
  • During incremental data migration, DTS creates a replication slot for the source database. 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 source ApsaraDB RDS for PostgreSQL instance, you must log on to the secondary instance to clear the replication slot.
    Replication slot information
  • 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. During full data migration, DTS uses read and write resources of the source and destination databases. This may increase the loads of the database servers.
  • During full data migration, concurrent INSERT operations cause fragmentation in the tables of the destination database. After full data migration is complete, the size of tablespace used by the destination database is larger than that of the source database.
  • You must make sure that the precision settings for columns of the FLOAT or DOUBLE data type meets your business requirements. DTS uses the ROUND(COLUMN,PRECISION) function to retrieve values from columns of the FLOAT or DOUBLE data type. If you do not specify a precision, DTS sets the precision for the FLOAT data type to 38 digits and the precision for the DOUBLE data type to 308 digits.
  • 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 used by DTS to access the destination instance. Otherwise, the data in the source database overwrites the data in the destination instance after the task is resumed.

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 completed, DTS migrates incremental data from the source database to the destination database. Incremental data migration ensures service continuity when you migrate data between self-managed databases.

SQL operations that can be migrated

Operation type SQL statements
DML INSERT, UPDATE, and DELETE

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

Before you begin

If the version of the self-managed PostgreSQL database is 10.1 to 13, you must perform the following operations before you configure a data migration task.
  1. Log on to the server where the self-managed PostgreSQL database resides.
  2. Set the value of the wal_level parameter in the postgresql.conf configuration file to logical.
    Set the wal_level parameter
  3. Add the CIDR blocks of DTS servers to the pg_hba.conf configuration file of the self-managed PostgreSQL database. Add only the CIDR blocks of the 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.
    Note For more information, see The pg_hba.conf File. Skip this step if you have set the IP address in the pg_hba.conf file to 0.0.0.0/0.
  4. 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.
If the version of the self-managed PostgreSQL database is 9.4.8 to 10.0, you must perform the following operations before you configure a data migration task.
  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. Go to the Data Migration page of the new DTS console.
    Note You can also log on to the Data Management (DMS) console. In the top navigation bar, click DTS.
  2. In the upper-left corner of the page, select the region in which the data migration instance resides.
  3. Click Create Task. On the page that appears, configure the source and destination databases.
    Warning After you select the source and destination instances, we recommend that you read the limits displayed at the top of the page. This helps you create and run the data migration task.
    Section Parameter Description
    N/A Task Name

    DTS automatically generates a task name. We recommend that you specify a descriptive name that makes it easy to identify. You do not need to use a unique task name.

    Source Database Database Type Select PostgreSQL.
    Access Method Select an access method based on the deployment of the source database. In this example, select Cloud Enterprise Network (CEN).
    Note If your source database is a self-managed database, you must deploy the network environment for the database. For more information, see Preparation overview.
    Instance Region Select the region where the self-managed PostgreSQL database resides.
    CEN Instance ID Select the ID of the CEN instance that hosts the self-managed PostgreSQL database.
    Connected VPC Select the virtual private cloud (VPC) that is connected to the self-managed PostgreSQL database.
    IP Address Enter the server IP address of the self-managed PostgreSQL database.
    Port Number Enter the service port number of the self-managed SQL Server database. The default port number is 1433.
    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.
    Destination Database Database Type Select PostgreSQL.
    Access Method Select Alibaba Cloud Instance.
    Instance Region Select the region where the destination ApsaraDB RDS for PostgreSQL instance resides.
    Instance ID Select the ID of the destination ApsaraDB RDS for PostgreSQL instance.
    Database Name Enter the name of the destination database in the ApsaraDB RDS for PostgreSQL instance.
    Database Account Enter the database account of the destination 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.

  4. In the lower part of the page, click Test Connectivity and Proceed.
    Warning
    • If the source or destination database instance is an Alibaba Cloud database instance, such as an ApsaraDB RDS for MySQL or ApsaraDB for MongoDB instance, or is a self-managed database hosted on Elastic Compute Service (ECS), DTS automatically adds the CIDR blocks of DTS servers to the whitelist of the database instance or ECS security group rules. 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 on data centers or is from other cloud service providers, you must manually add the CIDR blocks of DTS servers to allow DTS to access the database.
    • If the CIDR blocks of DTS servers are automatically or manually added to the whitelist of the database instance 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: enhance the security of your account and password, limit the ports that are exposed, authenticate API calls, regularly check the whitelist or ECS security group rules and forbid unauthorized CIDR blocks, or connect the database to DTS by using Express Connect, VPN Gateway, or Smart Access Gateway.
    • After the DTS task is completed or released, we recommend that you manually detect and remove the added CIDR blocks from the whitelist of the database instance or ECS security group rules.
  5. Configure objects to migrate and advanced settings.
    • Basic SettingsBasic 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 identical table names, the precheck is passed. Otherwise, an error is returned during 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 identical table 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 inconsistency may occur 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.
      Select Objects

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

      Note You can select columns, tables, or schemas as the objects to migrate. If you select tables or columns as the objects to migrate, DTS does not migrate other objects such as views, triggers, and stored procedures to the destination database.
      Rename Databases and Tables
      • 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.
      Filter data

      You can specify WHERE conditions to filter data. For more information, see Use SQL conditions to filter data.

      In the Selected Objects section, right-click an object. In the dialog box that appears, select the SQL operations that you want to migrate. For more information, see SQL operations that can be migrated.
    • Advanced SettingsAdvanced Settings
      Parameter Description
      Set Alerts
      Specify 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.
      • Select No if you do not want to set alerts.
      • Select Yes to set alerts. In this case, you must also set the alert threshold and alert contacts.
      Capitalization of Object Names in Destination Instance

      Specify 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 make sure that the capitalization of object names is consistent with that of the source or destination database. For more information, see Specify the capitalization of object names in the destination instance.

      Retry Time for Failed Connections
      Specify the retry time range for failed connections. Valid values: 10 to 720. Unit: minutes. Default value: 720. We recommend that you set the retry time range to more than 30 minutes. If DTS reconnects to the source and destination databases within the specified time range, DTS resumes the data synchronization task. Otherwise, the data synchronization task fails.
      Note
      • If an instance serves as the source or destination database of multiple data synchronization tasks, the value that is set later takes precedence.
      • 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 needs. You can also release the DTS instance at your earliest opportunity after the source and destination instances are released.
  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 various migration specifications. The migration speed varies based on the migration specifications that you select based on your business requirements. For more information, see Specifications of data migration instances.

  9. Read and select 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.