TABLE OF CONTENTS
- •Is moving to PostgreSQL right for you?
- •The Migration Decision at a Glance
- •Why Organizations Move to PostgreSQL
- •The Real Cost: License Savings Versus Migration Effort
- •Risk: Technical Differences
- •Coming from SQL Server
- •Coming from Oracle
- •Fit Analysis: How Hard Will the Migration Be?
- •Migration Tools
- •Migration Phases
- •When You Shouldn’t Move
- •Moving to PostgreSQL with Aryasoft
- •Frequently Asked Questions
- •Sources
- •Base your migration decision on data
Migrating from Oracle or SQL Server to PostgreSQL is a strategic decision that can remove license costs, but the real cost isn’t moving the data; it’s converting the code and testing it. Three factors decide whether a move makes sense: who owns the application (packaged software or your own development), how much database-specific code there is (stored procedures, triggers, packages) and how much downtime you can tolerate. This post explains how to weigh the decision in terms of cost, risk and fit.
The guide is for IT managers, architects and development teams considering PostgreSQL because of a license renewal, a cloud strategy or a modernization program.
Is moving to PostgreSQL right for you?
Aryasoft assesses your Oracle and SQL Server estate with an inventory and compatibility analysis and sets out the cost, risk and timeline of a move on the basis of data.
The Migration Decision at a Glance
| Situation | Assessment |
|---|---|
| Your own application, little database code | Strong candidate. The move is mostly data transfer and testing. |
| Your own application, heavy stored procedure and package code | Possible, but code conversion is the biggest line item; a detailed analysis is a must. |
| Packaged software (ERP, CRM and so on) | Only if the vendor officially supports PostgreSQL. Otherwise, don’t move. |
| Heavy use of Oracle-specific features (RAC, Advanced Queuing, Spatial and so on) | Each feature needs its own PostgreSQL assessment; some require architectural changes. |
| No PostgreSQL experience on the team | Settle the operating model before the move: training, external support or both. |
Why Organizations Move to PostgreSQL
- License cost: PostgreSQL has no license fee, and features aren’t restricted by edition. Commercial license costs climb fast as core counts grow, so the savings are biggest in large estates.
- Vendor independence: changes to a vendor’s pricing and licensing policy don’t affect you.
- Cloud portability: the same database runs in your own data center, on Azure, on AWS or on Google Cloud.
- Modern capabilities: JSON, geographic data (PostGIS) and vector search (pgvector) are available in the same database.
If you’re evaluating PostgreSQL for the first time, start with our What Is PostgreSQL? guide.
The Real Cost: License Savings Versus Migration Effort
The decision should compare license savings with the cost of migrating and operating.
| Item | What it includes |
|---|---|
| License savings | Current license and maintenance fees (Software Assurance, Oracle support); future core growth |
| Code conversion | Rewriting stored procedures, functions, triggers, packages and the SQL inside the application; usually the biggest item |
| Testing | Functional tests, performance tests, data validation; a large part of the project |
| Data transfer | Tools, migration time, downtime |
| Team and operations | Training, new monitoring and backup tools, a DBA with PostgreSQL experience or external support |
| Parallel running | Running both systems side by side during the transition |
Note
When you work out the payback period, count license savings as annual and migration cost as one-off. In estates with little code and high license costs, the move pays for itself quickly; in small estates with a lot of procedural code, the payback period can stretch out.
Risk: Technical Differences
Most surprises in migration projects come from features that look the same across databases but behave differently.
Coming from SQL Server
| Topic | SQL Server | PostgreSQL |
|---|---|---|
| Case sensitivity | Default collations are case-insensitive | Text comparison is case-sensitive by default |
| Object names | Case is preserved; square brackets | Unquoted names are folded to lower case; quoted names become case-sensitive |
| Procedural language | T-SQL | PL/pgSQL; different syntax and error handling |
| Auto-increment keys | IDENTITY | GENERATED AS IDENTITY or a sequence |
| Query syntax | TOP, ISNULL, GETDATE(), string concatenation with + | LIMIT, COALESCE, now(), string concatenation with || |
| Temporary tables | #temp tables | CREATE TEMP TABLE; different session scope |
| DDL and transactions | Most DDL runs inside a transaction | DDL is fully transactional and can be rolled back |
Coming from Oracle
| Topic | Oracle | PostgreSQL |
|---|---|---|
| Empty string and NULL | An empty string (”) is treated as NULL | Empty string and NULL are different; this is where most logic bugs come from |
| DATE type | Holds date and time | date holds only the date; the usual equivalent is timestamp(0) |
| NUMBER | One numeric type | Pick integer, bigint or numeric by usage; it affects performance |
| Packages | Available | Not available; redesigned with schemas and groups of functions |
| Hierarchical queries | CONNECT BY | Recursive CTE (WITH RECURSIVE) |
| Autonomous transactions | PRAGMA AUTONOMOUS_TRANSACTION | No direct equivalent; needs an architectural solution |
| Optimizer hints | Widely used | No built-in hint mechanism; queries and indexes are reworked |
Warning
The most insidious source of bugs in an Oracle migration is the difference between an empty string and NULL. In Oracle, WHERE column IS NULL also finds empty strings; in PostgreSQL it doesn’t. The application can return wrong results without raising an error, so data validation tests must check business rules, not just row counts.
Fit Analysis: How Hard Will the Migration Be?
The table below helps you roughly estimate a database’s migration complexity. If you tick “high” more than once, no timeline or budget should be given before a detailed assessment.
| Factor | Low | Medium | High |
|---|---|---|---|
| Database code | A few simple procedures | Hundreds of procedures and functions | Thousands of lines of procedural code, packages |
| Database-specific features | Standard SQL | Some proprietary functions | Deep dependence on platform-specific features |
| SQL in the application | Standard queries generated by an ORM | Mixed | Hand-written, platform-specific syntax |
| Data size | A few hundred GB | A few TB | Ten TB or more |
| Downtime tolerance | A weekend outage is acceptable | A few hours | Minutes |
| Integrations | One application | A few applications | Many systems, ETL, reporting |
Migration Tools
| Tool | What it does |
|---|---|
| ora2pg | Analyzes and converts Oracle schemas and code and produces a complexity report; open source |
| pgloader | Moves data from SQL Server and MySQL to PostgreSQL; open source |
| AWS Schema Conversion Tool and AWS DMS | Schema conversion and continuous data replication; for AWS targets |
| Azure Database Migration Service | Migration scenarios to Azure Database for PostgreSQL |
| Babelfish | A T-SQL compatibility layer on PostgreSQL, aiming to run SQL Server applications with fewer changes |
| Logical replication / CDC tools | Keep source and target in sync during the migration to shorten downtime |
Tools automate most of the schema and data transfer, but converting procedural code and validating business logic always needs expert review. “Converted automatically” in a tool report doesn’t mean the code works correctly.
Migration Phases
| Phase | What happens | Output |
|---|---|---|
| 1. Discovery | Inventory of databases, code, integrations and users | Inventory and scope |
| 2. Compatibility analysis | Tool reports, manual code review, complexity score | Cost and timeline estimate, decision |
| 3. Conversion | Converting the schema, data types, procedural code and application SQL | A working PostgreSQL schema |
| 4. Data transfer and sync | Initial load, then continuous transfer of changes | A target system in sync |
| 5. Testing | Functional, performance and data validation tests; parallel running | Acceptance report |
| 6. Cutover | Stop writes, final sync, repoint the application | PostgreSQL in production |
| 7. Stabilization | Close monitoring in the first weeks, performance tuning, keeping the rollback option open | A stable production environment |
We cover low-downtime migration methods and the rollback plan in our minimal downtime migration guide. To run PostgreSQL safely in production after the move, see our PostgreSQL best practices and high-availability PostgreSQL setup posts.
When You Shouldn’t Move
- When the application vendor doesn’t officially support PostgreSQL. Packaged software on an unsupported database puts your right to updates and support at risk.
- When the only reason is a short-term license renewal and the code conversion won’t fit into that window.
- When the team has no plan for running PostgreSQL. The license savings can easily be wiped out by the cost of outages.
Tip
In large, complex estates, a safer path than moving everything at once is to start new applications on PostgreSQL and migrate existing systems one by one, in order of risk.
Moving to PostgreSQL with Aryasoft
Aryasoft starts migration projects with an inventory and a risk analysis, run by a team with senior expertise in SQL Server, Oracle and PostgreSQL. When the complexity analysis is done, we also tell you plainly whether the move makes sense for you. If you decide to go ahead, we run the conversion, testing, a low-downtime cutover and the stabilization period with you. Details are on our database migration services and PostgreSQL services pages.
Frequently Asked Questions
Sources
The technical details in this guide were checked against the following sources in November 2026.
- PostgreSQL documentation: Porting from Oracle PL/SQL
- PostgreSQL documentation: Data Types
- PostgreSQL documentation: WITH Queries (Common Table Expressions)
- Ora2Pg
- pgloader documentation
- Babelfish for PostgreSQL
- Microsoft Learn: Migration service in Azure Database for PostgreSQL
- AWS Schema Conversion Tool
PostgreSQL Migration
Base your migration decision on data
Aryasoft analyzes your Oracle and SQL Server estate, sets out the cost, risk and timeline of the move, and runs the migration with a written rollback plan.
