As organizations evolve their data infrastructure, migrating from legacy database systems to modern, open-source alternatives has become increasingly common. This article explores two methods for migrating from IBM Db2 to PostgreSQL, a powerful and feature-rich open-source relational database management system. 

We'll examine an automated approach using Airbyte, a popular data integration platform, as well as a manual method leveraging Db2's db2look utility and PostgreSQL's COPY command. By understanding these migration strategies, database administrators and developers can choose the most suitable approach for their specific needs, ensuring a smooth transition while preserving data integrity and minimizing downtime.

Overview of IBM Db2

IBM Db2 is a family of data management products developed by IBM. It's a robust, enterprise-grade relational database management system (RDBMS) known for its reliability, scalability, and performance. Db2 supports various platforms, including mainframes, Unix, Linux, and Windows. It offers features like ACID compliance, high availability, and advanced security options, making it popular in large enterprises and mission-critical applications.

Overview of PostgreSQL

PostgreSQL, often called Postgres, is a powerful, open-source object-relational database system. It runs on all major operating systems and has a strong reputation for reliability, feature robustness, and performance. PostgreSQL is highly extensible and complies with SQL standards. It supports advanced data types and offers sophisticated features like Multi-Version Concurrency Control (MVCC), point-in-time recovery, and tablespaces.

Reasons for migrating from Db2 to PostgreSQL

1. Cost-effectiveness: PostgreSQL is open-source and free to use, potentially reducing licensing and support costs associated with Db2.

2. Open-source flexibility: Being open-source, PostgreSQL allows for greater customization and community-driven development.

3. Cross-platform compatibility: While Db2 has platform-specific versions, PostgreSQL offers consistent behavior across different operating systems.

4. Active community: PostgreSQL has a large, active community providing support, extensions, and frequent updates.

5. Scalability: PostgreSQL performs well in both small-scale and large-scale deployments.

6. Extensibility: PostgreSQL's extension ecosystem allows for easy addition of new functionalities.

7. Vendor independence: Moving to PostgreSQL reduces reliance on a single vendor (IBM), offering more flexibility in future database decisions.

These factors make PostgreSQL a better option for organizations looking to modernize their database infrastructure while potentially reducing costs and increasing flexibility.

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Methods to Move Data From IBM db2 to postgres 

• Method 1: Connecting IBM db2 to postgres using Airbyte.
• Method 2: Connecting IBM db2 to postgres manually.

Method 1: Connecting IBM db2 to postgres using Airbyte.

Prerequisites

Below are some prerequisites required for the tutorial.

• IBM Db2 –  You can install the executable from here or use the docker image *. In the examples presented in this tutorial, we use the docker image.
• Postgres – Download PostgreSQL to install it on your local host, or make use of a Postgres docker image.
• Open-source Airbyte – This can be locally installed using docker-compose.

* This tutorial was tested on an Apple Macintosh running X86 silicon.  At the time of writing, an ARM64-compatible Db2 docker image was not available, and so this does not work on newer ARM-based Macs.  

Step 1: Create a sample database table in IBM Db2

To migrate data from Db2 to Postgres, you must first create a sample table in the Db2 database. Using the Db2 docker image, you need to run the following series of commands to start the database engine and connect to it:

As discussed in the Docker Db2 Quick Start, start db2 as follows:

docker run -itd --name db2 --restart unless-stopped -e DBNAME=testdb -v /tmp/:/database -e DB2INST1_PASSWORD=MyP@$sw0rD -e LICENSE=accept -p 50000:50000 --privileged=true ibmcom/db2

Open a shell to the container:

docker exec -it db2 bash -c "su - db2inst1"

You should see a prompt similar to the following:

[db2inst1@8f2558dccbb0 ~]$

Use the db2 shell to connect to the testdb database:

db2
connect to testdb

Use the CREATE TABLE command to create a new table called FLOWER:

CREATE TABLE FLOWER (NAME VARCHAR(200), COLOR VARCHAR(200), FCOUNT INT)

Use the SQL INSERT INTO command to insert records into the FLOWER table as follows:

INSERT INTO FLOWER (name, color, fcount) VALUES ('Lily', 'White', 12),  ('Rose', 'Red', 1),  ('Lotus', 'Pink', 8),  ('Sunflower', 'Yellow', 9),  ('Daisy', 'White', 10),  ('Poppy', 'Red', 3),  ('Narcissus', 'Yellow', 12),  ('Blue Morning Glory', 'Blue', 10),  ('Chamomile Vine', 'Yellow', 19),  ('Scarlet', 'Red', 16)

Now that you have a populated Db2 database, you can use Airbyte to replicate your data!

Step 2: Set up IBM Db2 as an Airbyte source

After you have downloaded and followed the instructions to start Airbyte, you will be able to access the web UI through a browser on localhost:8000.

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You need to click the New Source button in the sources tab and select the Db2 source, after which some configuration details will be requested. Enter the values that were specified when the Db2 container was created, as follows:

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Once you enter all the details, click on the Setup Source button, which will connect to Db2 and validate your Airbyte source configuration.

Step 3: Start PostgreSQL

Next you will set up the destination and get it running before configuring Airbyte to use it. Start a container running PostgreSQL as follows:

docker run --rm --name postgres-destination -e POSTGRES_PASSWORD=password -p 3000:5432 -d postgres:13

Open a shell to the PostgreSQL container:

docker exec -it postgres-destination /bin/bash

Confirm that PostgreSQL is running using psql shell within the container:

psql -U postgres

Enter Ctrl+D to exit the psql shell.

Step 4: Setup PostgreSQL as an Airbyte destination

Now that PostgreSQL is running, you can set up PostgreSQL as an Airbyte destination. In the destination configuration, you will provide the  information that allows you to connect to the destination – complete the configuration as shown below, using the values that you specified when the PostgreSQL container was started:

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Step 5: Set up a Db2 to PostgreSQL connection

After setting up the source and the destination in Airbyte, you can choose to create a new connection, with the source and the destination that we have just created. You will then see a UI similar to the following:

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As can be seen in the image above, Airbyte has detected that the source database has a FLOWER table. For the sync mode, we have chosen Incremental |Append and have specified FCOUNT as the cursor field.

Click on the Set Up Connection button to complete the configuration, at which point the connection is established and will start syncing data.

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Once the sync is complete, you can verify if the data successfully landed in PostgreSQL. Let’s use the PostgreSQL shell (psql) to confirm as follows:

docker exec -it postgres-destination psql -U postgres

After connecting to the database, you can check all the available schemas and tables in the PostgreSQL database using the following command:

\dt *.*;

Airbyte has created a new table with the name flower. Next, you can check the data inside the flower table using the SELECT command as follows:

SELECT * FROM flower;

Which should respond with a table that looks similar to the following:

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The records from the Db2 database are now available in Postgres, including some additional metadata columns created by Airbyte.

If you were to execute additional syncs by pressing the Sync now button, you would see that only new records (i.e. records that have an FCOUNT value greater than the highest FCOUNT value in records that were previously replicated), will be copied. This is because we have chosen incremental replication with FCOUNT as the cursor. This is discussed in more detail in the tutorial: Explore Airbyte’s incremental data synchronization.

Method 2: Connecting IBM db2 to postgres manually

Moving data from IBM DB2 to PostgreSQL without using third-party connectors or integrations can be a challenging task. Below is a step-by-step guide to facilitate this process using the tools provided by both DBMSs. This guide assumes you have administrative access to both the DB2 and PostgreSQL databases and the necessary permissions to execute data export and import operations.

Step 1: Environment Setup

Ensure that both the IBM DB2 and PostgreSQL database servers are properly installed and configured on their respective systems. Install the required database drivers and command-line tools for both DBMSs.

Step 2: Schema Migration

Before you can move data, you need to recreate the DB2 schema in PostgreSQL. This involves creating tables, indexes, views, and other database objects.

1. Extract the DB2 database schema:

   Use the `db2look` utility to extract the database schema from DB2:

   ```sh

   db2look -d your_db2_database -e -o db2_schema.sql

   ```

   This command will generate a SQL file `db2_schema.sql` with the DDL statements for the DB2 database.

2. Modify the schema for PostgreSQL compatibility:

   Edit the `db2_schema.sql` file to make it compatible with PostgreSQL. This may involve changing data types, removing DB2-specific syntax, and adjusting SQL functions and stored procedures.

3. Create the PostgreSQL schema:

   Execute the modified schema SQL script against your PostgreSQL database to create the schema:

   ```sh

   psql -U postgres_user -d postgres_database -f modified_db2_schema.sql

   ```

Step 3: Data Export from DB2

You will need to export the data from DB2 into a format that can be imported into PostgreSQL.

1. Export the data using the `db2export` command:

   ```sh

   db2 "export to tablename.ixf of ixf messages tablename.msg select * from tablename"

   ```

   Replace `tablename` with the actual table name. The `.ixf` format is a proprietary IBM format, but we will convert it in the next step.

2. Convert the .ixf file to a delimited format (e.g., CSV):

   Use the `db2` command line or a custom script to convert the `.ixf` files to a CSV format that PostgreSQL can understand.

Step 4: Data Import into PostgreSQL

Now that you have the data in a CSV format, you can import it into PostgreSQL.

1. Copy the CSV files to the PostgreSQL server:

   Use `scp`, `ftp`, or any other file transfer method to move the CSV files to the PostgreSQL server.

2. Import the data using the `psql` command:

   Use the `\copy` command within `psql` to import the data:

   ```sh

   psql -U postgres_user -d postgres_database

   \copy tablename from 'tablename.csv' with (format csv, header true, delimiter ',');

   ```

   Replace `tablename.csv` with the actual CSV filename and adjust the delimiter and header options as needed.

Step 5: Verify Data Integrity

After importing the data, it's essential to verify that the data has been transferred correctly.

1. Check record counts:

   Compare the record counts in both DB2 and PostgreSQL for each table to ensure they match.

2. Perform data checks:

   Execute queries to check for data consistency and integrity between the source DB2 and target PostgreSQL databases.

3. Check for errors:

   Review the import logs for any errors or warnings that may indicate issues with the data import.

Step 6: Finalize the Migration

Once you're satisfied with the data integrity, you can finalize the migration by:

1. Updating sequences:

   If you have any auto-increment columns, update the sequences in PostgreSQL to reflect the current state.

2. Performing optimizations:

   Analyze the tables and indexes in PostgreSQL to optimize their performance.

3. Testing applications:

   Update your application connection strings and thoroughly test your applications with the new PostgreSQL database.

Step 7: Clean Up

After the migration is successfully completed and verified, clean up any temporary files or scripts used during the migration process.

This guide provides a high-level overview of the steps involved in migrating data from IBM DB2 to PostgreSQL without third-party tools. Due to the complexity of such a task, you may encounter specific challenges related to your data and schema that require additional manual adjustments and troubleshooting. Always perform a backup before starting the migration process and test thoroughly in a non-production environment.

IBM Db2 to PostgreSQL Pre-migration Checklist

To prepare for migrating from IBM Db2 to PostgreSQL, follow these key steps:

1. Assess current Db2 environmentsome text
   • Document database size, schema structure, and data types
   • Identify custom functions, stored procedures, and triggers
   • List all applications and services using the database
2. Analyze compatibilitysome text
   • Compare Db2 and PostgreSQL data types, functions, and syntax
   • Identify potential issues with data type conversions
   • Check for Db2-specific features without direct PostgreSQL equivalents
3. Plan the migrationsome text
   • Decide on migration method (Airbyte or manual)
   • Set a timeline and allocate resources
   • Determine acceptable downtime window
   • Create a rollback plan
4. Set up target environmentsome text
   • Install and configure PostgreSQL
   • Ensure sufficient storage and computing resources
   • Set up network access and security measures
5. Create test environmentsome text
   • Set up a smaller-scale version of both Db2 and PostgreSQL
   • Practice migration process on a subset of data
6. Plan for data validationsome text
   • Develop process to compare data before and after migration
   • Establish criteria for successful migration
7. Communicate with stakeholderssome text
   • Inform all affected parties about the migration plan
   • Coordinate with application teams for testing and cutover
8. Perform dry runssome text
   • Execute the full migration process in a test environment
   • Refine procedures based on results

Wrapping Up

This tutorial has demonstrated the following:

1. Start a container running IBM Db2
2. Configure an Airbyte source to replicate data from Db2.
3. Start a container running PostgreSQL.
4. Configure a PostgreSQL as an Airbyte destination.
5. Create an Airbyte connection that syncs data from Db2 to PostgreSQL.

If you liked this tutorial, you might also consider browsing Airbyte’s blog or other tutorials. You can also participate in conversations on Airbyte's discourse, join our community Slack channel, or subscribe to our newsletter. Additionally, you may test out Airbyte Cloud if you're interested in Airbyte as a fully managed service!