Marek is available for hire
Hire MarekMarek Rozenbajger
Verified Expert in Engineering
Data Architect and ETL Developer
Gdańsk, Poland
Toptal member since August 29, 2016
Bio
Marek has spent his whole professional life working with data. Coming from a Microsoft data warehousing background, he joined big data transformation in 2017. Throughout his career, he has worked as a data architect, senior consultant, and lead programmer for UBS, BP, Honda, and Motorola. Marek has over a decade of experience working in distributed teams. Nowadays, he focuses on modeling and designing data lake-houses on the Microsoft Azure platform and open source stack: Airflow and PostgreSQL.
Portfolio
Wiretouch Ltd
Azure SQL Databases, SQL, Azure, SQL Performance, Database Performance...
Fincent Inc
Relational Databases, Data Warehouse Design, PostgreSQL, Database Modeling...
UBS
Microsoft SQL Server, Python 3, PySpark, Azure Databricks, Azure...
Experience
- Database Modeling - 17 years
- SQL - 17 years
- Transact-SQL (T-SQL) - 16 years
- Data Modeling - 13 years
- ETL Development - 13 years
- Data Warehousing - 13 years
- Data Warehouse Design - 9 years
- Data Lake Design - 3 years
Preferred Environment
Git, Visual Studio, Windows Server, Microsoft SQL Server, Azure Blob Storage API
The most amazing...
...thing I've designed was a data lakehouse with 30 bitemporal, slow-changing dimensions and late-arriving facts of different granularity with M2M relationships.
Work Experience
SQL/Azure Database Expert
2025 - 2025
Wiretouch Ltd
- Designed a 3NF schema consisting of partitioned tables and supporting objects.
- Implemented migration from code-first Entity Framework-generated Microsoft SQL Server database to the designed schema.
- Planned and prepared a release by accounting for the minimal possible production downtime requirement. Prepared a set of heavily customized SSDT change scripts.
Technologies: Azure SQL Databases, SQL, Azure, SQL Performance, Database Performance, Scalability, Database Partitioning, Databases, Tools, Relational Database Design
Data Engineer
2021 - 2022
Fincent Inc
- Designed a complete data platform, including the dimensional model, data lake, orchestration, and ELT pipelines. Used Postgres, Apache Airflow, S3, and Python for the tech stack.
- Provided architectural documentation of the solution with guidelines for usage and future extensions.
- Performed the MVP implementation of the data platform. Used MWAA for orchestrating ELT, RDS for metadata database, and S3 for storage.
Technologies: Relational Databases, Data Warehouse Design, PostgreSQL, Database Modeling, Sparx Enterprise Architecture, Python 3, Data Lake Design, Data Warehousing, Amazon Web Services (AWS), Pandas, ETL, Apache Airflow, UML, Git, JSON, Data Modeling, Python, REST APIs, ETL Development, ELT, Data Pipelines, Data Lakes, ETL Tools, Big Data Architecture, Database Architecture, Data Architecture, RDBMS, Databases, SQL, Database Design, Amazon RDS, System Administration, Consulting, Data Management, Normalization, SQL Stored Procedures, Database Structure, Database Transactions, Transactions, Data, Data Cleaning, Data Aggregation, APIs, Requirements Analysis, GitHub, CSV File Processing, Data Processing, Data Cleansing, Star Schema, Finance, Apache Spark, Data Transformation, Relational Database Design
Senior BI Consultant | Data Architect
2016 - 2022
UBS
- Designed serverless architecture for Azure data lakehouse with Power BI, Azure Databricks, Azure Functions, ADLS Gen2, and Azure Data Factory. Used Spark SQL, Python, and PowerShell programming.
- Provided data modeling and profiling activities for projects and created visual models of data flows and interactions with UML, DFD, and ERD.
- Designed and implemented state machine-based orchestration for the data lake.
- Supported and extended Microsoft SQL Server data warehouses.
- Created end-to-end CI/CD automation for Microsoft SQL server data warehouse.
Technologies: Microsoft SQL Server, Python 3, PySpark, Azure Databricks, Azure, Microsoft Power BI, SQL Server BI, UML, Spark, Spark SQL, Windows PowerShell, Azure Data Factory (ADF), Azure Functions, Data Warehousing, Data Warehouse Design, Data Lake Design, Database Modeling, Bitemporality, ELT, ETL, Relational Databases, Transact-SQL (T-SQL), Windows Server 2012, Continuous Integration (CI), Databricks, JSON, Data Modeling, Python, REST APIs, OData, ETL Development, Pandas, Data Pipelines, Azure Data Lake, Data Lakes, Big Data, ETL Tools, Big Data Architecture, BI Reporting, Business Intelligence (BI), Database Architecture, Data Architecture, SQL Server DBA, RDBMS, Databases, Oracle, SQL, Database Design, SQL Server 2016, Reports, Consulting, Data Management, Data Visualization, Data Wrangling, Normalization, SQL Stored Procedures, Database Optimization, Database Structure, Database Transactions, Transactions, Data, Data Cleaning, Data Aggregation, Azure SQL, Performance Tuning, Requirements Analysis, CSV File Processing, Kubernetes, Data Processing, Azure Blob Storage API, DAX, Azure SQL Databases, Database Performance, SQL Performance, Database Partitioning, Data Cleansing, Reporting, Star Schema, Finance, Apache Spark, Data Transformation, Relational Database Design
Database Consultant
2020 - 2021
Honda
- Reverse-engineered a legacy Microsoft Access-based ERP system; no source code was available.
- Designed a new solution that improved on the original. The application consisted of Windows Forms UI, relational database, and reports components.
- Went through the complete SDLC cycle: implemented the design, tested it, and released it. The client was pleased and requested several new features to be added as a separate project.
Technologies: SQLite, .NET, SQL, Windows Forms (WinForms), C#, Microsoft Visual Studio, Visual Basic for Applications (VBA), Git, Microsoft Excel, Database Modeling, Object-oriented Design (OOD), Object-relational Mapping (ORM), SQLite.NET, JSON, Data Engineering, Relational Databases, Microsoft Access, Data Analysis, Data Reporting, Database Architecture, RDBMS, Databases, Database Design, Reports, Consulting, Excel VBA, Normalization, Database Structure, Transactions, OLTP, Data, Requirements Analysis, CSV File Processing, Data Migration, Reporting, Finance, Relational Database Design
Database Consultant
2018 - 2018
The Dominion Group
- Created a custom add-in for Excel 2010 and above. The add-in provides a set of functions that pull data from remote PostgreSQL instances over the Internet.
- Tested the product with different Microsoft Office versions: 2010, 2016, 2019, 365.
- Prepared documentation: PDF and user training videos.
- Answered users' queries and provided support for the application.
Technologies: PostgreSQL, Microsoft Excel, Relational Databases, SQL, C#, Microsoft Visual Studio, .NET, Git, SQLite, Database Modeling, Object-oriented Design (OOD), Object-relational Mapping (ORM), ODBC, SQLite.NET, JSON, Data Engineering, Data Analysis, Data Reporting, Database Architecture, RDBMS, Databases, Database Design, Reports, Consulting, Excel VBA, Visual Basic for Applications (VBA), Normalization, Database Structure, Data, Requirements Analysis, CSV File Processing, Data Migration, Reporting, Relational Database Design
Software Developer
2017 - 2018
Motorola Solutions
- Worked with the key stakeholder on clarifying and documenting the requirements.
- Designed the solution for a sophisticated near-real-time directory change monitoring service.
- Prepared the documentation and provided support for service rollout.
Technologies: C#, SQLite, Azure Active Directory, Relational Databases, SQL, Microsoft Visual Studio, Windows Server, .NET, Git, Microsoft Excel, Database Modeling, Object-oriented Design (OOD), Windows Server 2012, SQLite.NET, JSON, Data Engineering, Data Analysis, Data Reporting, Database Architecture, RDBMS, Databases, Database Design, Reports, Database Structure, OLTP, Requirements Analysis, Data Transformation
Database Consultant
2016 - 2016
Nordea Group
- Carried out an audit of a bespoke database system.
- Implemented a feasibility study of new requirements and risk analysis.
- Provided a review of the system to the management of the project.
Technologies: Relational Databases, SQL, Microsoft Visual Studio, Microsoft Excel, Database Modeling, Data Engineering, Database Architecture, RDBMS, Databases, Database Design, Consulting, Normalization, Database Structure, Transactions, OLTP, Data, Requirements Analysis, Data Migration, Finance, Relational Database Design
Data Architect | Solution Architect
2012 - 2016
BP p.l.c.
- Designed and had a key role in the implementation of a data warehouse. Its purpose was to improve financial efficiency by providing reports and data for analysis.
- Created and implemented the system architecture, database back-end, and ETL and WCF API design.
- Developed the modeling process which concentrated on UML (use case, class, sequence diagrams) as well as data flow, and entity-relationship diagrams.
- Built a database component that involved advanced programming features of Microsoft SQL Server such as CLR integration, distributed transactions, and XML processing.
- Designed and managed the implementation of a self-service intranet site for managing IT services (such as mailboxes, user accounts, distribution lists, and VPN tokens) for 80,000 employees. The purpose of the site was to support the ITIL processes.
- Designed and implemented the system architecture, database design, integration with external systems (LDAP, SOAP web services, REST web services, ODBC), WCF API of the back-end component, and long-running workflows.
- Built a system using Windows Server 2008 R2 Standard, WCF SOAP web services, and an active directory with Kerberos authentication, IIS AppFabric 1.1, and C#.NET 4.0.
- Prepared implementation documentation for the client.
- Liaised with the client's technical authorities and infrastructure managers.
Technologies: Windows Server, Microsoft SQL Server, Relational Databases, SQL, SQL Server 2008, Azure Active Directory, UML, C#, SQL CLR, SQL Server 2012, Data Warehouse Design, SOAP, Microsoft Visual Studio, Windows Server 2008, .NET, Windows PowerShell, SQL Server Integration Services (SSIS), Git, Database Modeling, SQL Server Reporting Services (SSRS), SQL Server Data Tools (SSDT), LDAP, Kerberos, SSAS, Object-oriented Design (OOD), Object-relational Mapping (ORM), Sparx Enterprise Architecture, Kimball Methodology, Continuous Integration (CI), OLAP, ODBC, MDX, JSON, Data Engineering, Windows Forms (WinForms), Transact-SQL (T-SQL), Data Warehousing, Data Modeling, REST APIs, ETL Development, ETL, SQL Server BI, Data Pipelines, ETL Tools, BI Reporting, Business Intelligence (BI), Database Architecture, Data Architecture, RDBMS, Databases, Database Design, Data Visualization, Data Wrangling, Normalization, SQL Stored Procedures, Database Structure, Database Transactions, Transactions, Data, Data Cleaning, Data Aggregation, APIs, Requirements Analysis, CSV File Processing, Data Processing, Database Performance, SQL Performance, Database Partitioning, Data Cleansing, Reporting, Star Schema, Database Replication, Data Transformation, Relational Database Design
Database Administratior | SQL Developer
2008 - 2012
BP p.l.c.
- Migrated a reporting platform from the Microsoft SQL Server 2000 to the 2005 version and later to 2008 R2.
- Designed and implemented new data feeds into the reporting system.
- Designed new reports for mid-level managers and enriched the existing ones with additional data.
- Maintained and adapted the system to new requirements and a changing environment.
Technologies: C#, Microsoft SQL Server, Relational Databases, SQL, SQL Server 2008, SQL CLR, Microsoft Visual Studio, Windows PowerShell, SQL Server Integration Services (SSIS), PostgreSQL, Database Modeling, SQL Server Reporting Services (SSRS), LDAP, SSAS, Object-oriented Design (OOD), Database Administration (DBA), ODBC, MDX, Transact-SQL (T-SQL), Data Analysis, Data Reporting, Business Intelligence (BI), Database Architecture, SQL Server DBA, RDBMS, Databases, Oracle, Database Design, System Administration, Reports, Visual Basic, Normalization, SQL Stored Procedures, Database Optimization, Database Structure, Database Transactions, Data, Performance Tuning, Requirements Analysis, CSV File Processing, Database Migration, Data Processing, Database Performance, SQL Performance, Database Partitioning, Data Migration, Reporting, Star Schema, Data Transformation, Relational Database Design
Microsoft Access Database Developer
2006 - 2008
Ideal Shopping Direct
- Developed applications for stock control, EDI, work time and performance monitoring with Microsoft Access (VBA) and Microsoft SQL Server (backend).
- Created reports from the collected data with Microsoft Access and Excel (automatic generation of spreadsheets from VBA code).
- Improved several manual processes with the help of self-developed applications.
Technologies: Microsoft Excel, Microsoft Access, Visual Basic for Applications (VBA), Relational Databases, SQL, Visual Basic .NET (VB.NET), Database Modeling, Database Architecture, RDBMS, Databases, Database Design, Reports, Data Visualization, Visual Basic, Excel VBA, Normalization, Database Structure, Data, Requirements Analysis, Relational Database Design
Experience
Sample Data Warehouse Snowflake Schema ERD
I implemented tables designed to store comprehensive information within a larger model. This model utilizes slowly changing dimensions of type 2 and type 1, ensuring effective management of evolving data over time. The schema follows a fully normalized approach, representing a design philosophy predating the era of massively parallel processing (MPP).
Sample 3NF Entity Relationship Diagram
I developed a professionally designed relational schema to store computer hardware information. This model was implemented on the MS SQL platform some time ago, employing a strictly normalized model.
Based on this schema, the system has demonstrated durability and longevity, successfully serving its intended purpose for a significant period. It is rumored to continue functioning reliably even today, attesting to the effectiveness and robustness of the original design and implementation.
Based on this schema, the system has demonstrated durability and longevity, successfully serving its intended purpose for a significant period. It is rumored to continue functioning reliably even today, attesting to the effectiveness and robustness of the original design and implementation.
Sample Data Dictionary
I compiled a comprehensive data dictionary encompassing a detailed description of a computer and user database. This particular stub was generated utilizing Visual Paradigm software, which I proficiently employed during a previous period.
While I lean towards using Sparx EA, it is worth noting that the data dictionary generated from Visual Paradigm showcases an elegant and well-structured representation of the database schema. It effectively captures essential information and is a valuable reference for understanding the database's various entities, attributes, relationships, and constraints.
While I lean towards using Sparx EA, it is worth noting that the data dictionary generated from Visual Paradigm showcases an elegant and well-structured representation of the database schema. It effectively captures essential information and is a valuable reference for understanding the database's various entities, attributes, relationships, and constraints.
Education
2008 - 2012
Bachelor's Degree in Computer Science
The School of Banking and Management in Kraków - Kraków, Poland
Certifications
JANUARY 2010 - PRESENT
MCP: Windows Server
Microsoft
JANUARY 2010 - PRESENT
MCTS: SQL Server 2008
Microsoft
JANUARY 2009 - PRESENT
ITIL Foundation
Asseco Data Systems
Skills
Libraries/APIs
ODBC, SQLite.NET, PySpark, Windows Forms (WinForms), REST APIs, Pandas, Azure Blob Storage API
Tools
Microsoft Access, Microsoft Excel, SSAS, Spark SQL, Microsoft Power BI, Apache Airflow, Microsoft Visual Studio, GitHub, Git, SQL Server BI, Visual Paradigm
Languages
Transact-SQL (T-SQL), SQL, UML, C#, Python 3, MDX, Visual Basic for Applications (VBA), Visual Basic .NET (VB.NET), Python, Visual Basic, Excel VBA
Paradigms
Business Intelligence (BI), Database Design, OLAP, Object-oriented Design (OOD), Object-relational Mapping (ORM), ETL, Requirements Analysis, Kimball Methodology, Continuous Integration (CI), Management
Platforms
Databricks, Azure, Windows Server, Windows Server 2008, Windows Server 2012, Azure Functions, Amazon Web Services (AWS), Oracle, Kubernetes
Storage
Microsoft SQL Server, Database Modeling, Relational Databases, SQL Server Data Tools (SSDT), SQL Server 2008, SQL Server Reporting Services (SSRS), Data Pipelines, Database Architecture, RDBMS, Databases, SQL Server 2016, SQL Stored Procedures, Database Structure, Database Transactions, Azure SQL Databases, SQL Performance, SQLite, PostgreSQL, Database Administration (DBA), Azure Active Directory, SQL Server 2012, SQL CLR, JSON, Data Lake Design, Data Lakes, Azure SQL, Database Performance, SQL Server Integration Services (SSIS), SQL Server DBA, OLTP, Database Migration, Database Replication
Frameworks
Spark, Apache Spark, Windows PowerShell, .NET
Other
Data Engineering, Data Warehousing, Data Modeling, ETL Development, Azure Databricks, ETL Tools, Data Reporting, Data Architecture, Data Wrangling, Normalization, Transactions, Data, Data Cleaning, Data Aggregation, CSV File Processing, Data Processing, Data Cleansing, Reporting, Star Schema, Data Transformation, Relational Database Design, Kerberos, LDAP, OData, Azure Data Factory (ADF), Azure Data Lake, Data Analysis, BI Reporting, Reports, APIs, Database Partitioning, Data Migration, Data Warehouse Design, Sparx Enterprise Architecture, SOAP, Big Data Architecture, Bitemporality, ELT, Big Data, Amazon RDS, System Administration, Consulting, Data Management, Data Visualization, Database Optimization, Performance Tuning, DAX, Finance, Scalability, Tools
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