Re: Guidance Requested: Migrating Large-Scale DB2 Databases to PostgreSQL - Mailing list pgsql-admin

A few other points I’d like to highlight — we use the DB2 LOAD utility for our daily data loads into tables. Since this utility bypasses transaction logging for performance reasons, any open-source replication tool that relies on transaction logs to replicate data into PostgreSQL will not capture or replicate these changes. Therefore, I'm looking for tools that can specifically address this primary limitation.

On Sat, Oct 18, 2025 at 1:19 AM mahamood hussain <hussain.ieg@gmail.com> wrote:

Hi Brian, Ron, Kurtoglu,

Thank you all for the thoughtful responses. It took a bit of effort to pull this information together, but I'm glad to see the insights coming in — it's given me more confidence that this migration is indeed achievable with the right approach.

To clarify our setup:
We're currently running DB2 LUW v11.5.9 (Advanced Enterprise Server Edition). One of our key concerns is licensing cost, which is driving our move to PostgreSQL.

A few follow-up questions based on your responses:

1. InfoSphere Data Replication (CDC):
   We understand this is a strong option, but it likely incurs additional licensing costs. We’re exploring Fivetran for data replication between DB2 and PostgreSQL, with the flexibility to fall back to DB2 if performance or stability issues arise in production.

   • Can CDC be used for such a failback scenario (i.e., from PostgreSQL → DB2) similar to how Fivetran supports bidirectional sync?

2. Open-source Tools:
   Do we have any robust open-source tools  that support both forward and backward replication between DB2 and PostgreSQL? This would help us plan for both migration and rollback scenarios without heavy vendor lock-in.

3. Pitfalls to Avoid During Migration:
   Since our primary goal is cost reduction, we would ideally avoid needing to fall back to DB2. Based on your experience, what are some common pitfalls or gotchas we should look out for when moving from DB2 to PostgreSQL?

4. PostgreSQL Performance Tuning & Config:
   If there’s a list of standard PostgreSQL parameters  that you'd recommend tweaking right after installation — especially for large datasets — that would be very helpful. We're anticipating around 100+ concurrent connections during peak hours and migrating some very large tables (up to 80B rows).

5. Community vs Enterprise Support:
   In production, having support with a guaranteed response time (e.g., under an hour) is crucial.

   • Does the PostgreSQL community offer any premium or paid support options with SLAs, or would we need to go with providers like EDB for this level of assurance?

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On Thu, Oct 16, 2025 at 6:15 PM Brian Crockard <bcrockard@yahoo.com> wrote:

You may want to look into an IBM product called InfoSphere Data Replciation (CDC)

https://www.ibm.com/docs/nl/idr/11.4.0?topic=requirements-supported-source-targets

It will replicate data from DB2 to PostgreSQL. You can set it up to actively replciate the data and keep it consistent. Then perform a cutover at some point to the new system running against the new replicated database. You will then have all of your historical data in the new system. We used this on an extremely active system and it hard very few issues. 

On Wednesday, October 15, 2025 at 05:15:00 PM EDT, mahamood hussain <hussain.ieg@gmail.com> wrote:

Hi Team,

We are in the process of migrating several DB2 databases to PostgreSQL, primarily to reduce the high licensing costs associated with DB2. These databases support retail applications (e.g., supermarkets and stores), and during peak hours, we anticipate over 100 concurrent connections.

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Current Database Profile:

• Approximately 3,000 tables in total

• Around 100 tables contain active data

• Most tables have low data volume

• A few large tables range from 10 GB to 2 TB

• The largest table contains approximately 80 billion rows

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Migration Approach:

• We are using Ispirer for code conversion (DB2 to PostgreSQL).

• For data migration, we are evaluating Fivetran, but noted that it relies on the COPY method for data loading.

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Questions & Areas Where We Need Guidance:

1. Is Fivetran a suitable option for migrating very large datasets (e.g., tables with 80+ billion rows)?

2. Are there any reliable open-source tools for DB2 to PostgreSQL data migration that we can use internally, without needing to invest in a tool like Fivetran?

3. Are there more scalable or efficient alternatives for both the initial load and ongoing/incremental sync to PostgreSQL?

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Additional Input Requested:

• What are the key best practices (Do’s and Don’ts) to keep in mind during a large-scale DB2 → PostgreSQL migration?

• Are there specific PostgreSQL settings or configurations we should pay attention to for optimizing performance, especially for large datasets and DB2-style workloads?

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We are keen to ensure performance, data integrity, and scalability throughout this migration. Any insights—particularly from those with experience in similar large-scale PostgreSQL implementations—would be highly appreciated.

If this is not the right forum for these questions, please do let me know if there is a better place to seek this guidance.

Thanks in advance for your support!