Senior Data Engineer: High-Throughput Java & Kafka Pipelines

Who is Hiring; Warszawa; On-site; PLN 240,000 - 420,000; Full time

Job summary

Who is Hiring in Warszawa, Poland, seeks a senior backend engineer to design and maintain distributed, high-throughput systems. You will build production-grade Java services, optimize Kafka and Flink pipelines, and integrate data across products using PostgreSQL, ClickHouse and Redis.

You will also implement APIs with gRPC/Protobuf, collaborate with architecture, product and DevOps teams, and ensure observability, security and code quality in a fast-moving enterprise environment.

Qualifications

• 6+ years of experience building and maintaining production distributed, high-throughput systems.
• 5+ years of professional Java experience, including concurrency, memory management and JVM performance tuning.
• 3+ years of hands-on production experience with Apache Kafka, including partitioning, consumer groups, schemas, delivery guarantees, fault tolerance and throughput tuning.
• 2+ years of hands-on production experience with Apache Flink, including stateful processing, windowing, checkpointing, state management, backpressure and fault recovery.
• Proven track record of personally building, scaling and operating systems processing millions of events per minute.
• Deep understanding of time-series and large-scale analytical databases, including modeling, ingestion, query tuning and partitioning.
• Hands-on experience with PostgreSQL or another relational database.
• Strong command of Protobuf, including schema evolution and compatibility.
• Working knowledge of gRPC and service-to-service communication.
• Hands-on experience deploying, monitoring and troubleshooting distributed workloads on Kubernetes.
• Hands-on experience with Docker and CI/CD pipelines.
• Solid understanding of production observability and incident resolution.
• Hands-on use of AI-assisted and agentic coding tools in production, including critical review of generated code.
• Proven ability to deliver independently, make architectural tradeoffs and identify risks early.
• Strong communication skills for explaining technical decisions and working with international teams.
• English -- Upper-Intermediate
• Would Be a Plus
• Hands-on experience with ClickHouse
• Hands-on experience with Redis
• Hands-on experience with TypeScript and React

Responsibilities

• Build production-grade Java services and high-throughput data-processing components
• Develop, optimize and maintain large-scale Kafka and Apache Flink streaming pipelines
• Integrate data from multiple products into a unified organizational data model
• Implement employee, department, device and RBAC-related functionality
• Build services and APIs using Java, TypeScript, gRPC and Protobuf
• Design and optimize persistence on PostgreSQL, ClickHouse and Redis, including schemas, indexes and data-access patterns
• Improve scalability, reliability, throughput, latency, observability and operational cost
• Diagnose production bottlenecks across distributed pipelines, services and databases
• Develop TypeScript and React frontend capabilities when needed
• Collaborate with architecture, product and DevOps teams
• Use AI-assisted and agentic development tools while maintaining correctness, security and code quality

Skills

Distributed systems

Java

Apache Kafka

Apache Flink

Scaling systems

Time-series DBs

PostgreSQL

Protobuf

gRPC

Kubernetes

Docker

CI/CD

Observability

AI-assisted coding

Architectural tradeoffs

Communication

ClickHouse

Redis

TypeScript

React

Tools

Kafka

Flink

PostgreSQL

ClickHouse

Redis

Protobuf

gRPC

Kubernetes

Docker

CI/CD

TypeScript

React

Job description

Who is Hiring in Warszawa, Poland, seeks a senior backend engineer to design and maintain distributed, high-throughput systems. You will build production-grade Java services, optimize Kafka and Flink pipelines, and integrate data across products using PostgreSQL, ClickHouse and Redis.

You will also implement APIs with gRPC/Protobuf, collaborate with architecture, product and DevOps teams, and ensure observability, security and code quality in a fast-moving enterprise environment.