Senior Database Architect (SQL Server & PostgreSQL) - B2B / Freelancers

Xebia is a global AI-first, digital transformation, and engineering partner. With over 25 years of experience and a team of 5,000 professionals across 16 countries, we help organizations design and build scalable products, platforms, and data-driven solutions. We specialize in Artificial Intelligence, Data and Cloud, Intelligent Automation, and Digital Products, combining deep technical expertise with a strong focus on engineering excellence and a people-first culture. In the CEE region, we’re a team of nearly 1,000 experts delivering modern applications, data platforms, and AI solutions for clients such as McLaren, Aviva, Deloitte, Spotify, Disney, ING, UPS, Tesco, Truecaller, AllSaints, Volotea, Schmitz Cargobull, Allegro, InPost, and many, many more. We work with leading technologies including AWS, Azure, GCP, Databricks, and Snowflake, and combine strong engineering culture with a consulting mindset and a continuous focus on growth and knowledge sharing. Our client is a software company running a large, business-critical ERP system used to support core operational processes such as payroll, billing and workforce scheduling. The organisation is in the middle of a multi-year modernisation programme, moving away from a legacy technology stack toward a modern .NET/web-based platform, while keeping the legacy system fully operational in production throughout the transition. Contract: B2B or Freelance You will be: Strong, hands-on SQL Server expertise (design, indexing, query optimisation, operational practices). Solid working knowledge of PostgreSQL, sufficient to assess migration feasibility and compatibility. Proven experience optimising query and index performance in production environments. Experience modernising or refactoring databases behind legacy applications. Ability to define and set up database observability/monitoring (baselines, diagnostics, wait stats, deadlock detection, alerting). A pragmatic, risk-aware approach that balances improvement effort against migration cost and business risk. Your profile: Experience assessing and scoping SQL Server → PostgreSQL migrations (not necessarily having executed a full migration). Experience working in environments where legacy and modern systems coexist in production during a transition. Comfort working with Specification-Driven Development (SDD) frameworks such as OpenSpec, or similar structured requirements/traceability approaches. Ability to produce clear, prioritised, business-readable recommendations for non-DBA stakeholders. Work from the European Union region and a work permit are required. Tasks Review the current SQL Server database design, indexes, queries and operational practices. Identify performance issues, technical debt, risks and areas that are already working well. Recommend and prioritise pragmatic improvements. Assess the feasibility of migrating from SQL Server to PostgreSQL — identifying compatibility issues, risks, expected effort and possible migration approaches. Define and implement robust database observability and performance monitoring, including performance baselines, query-level diagnostics, wait statistics, blocking/deadlock detection, capacity trends and actionable alerting. Work within an AI-native engineering environment, using Specification-Driven Development (SDD) frameworks such as OpenSpec to structure requirements, implementation plans, validation and traceability. Nice to have: Prior exposure to legacy 4GL or transpiled/generated codebases. Familiarity with .NET/Blazor application ecosystems as a consumer of the data layer. Experience with database-heavy ERP systems (payroll, billing, scheduling domains). Experience in AI-assisted/AI-native engineering workflows more broadly. Recruitment Process: CV review – HR call – Interview – Client Interview – Decision