Marko Topolnik
Senior Software Engineer at QuestDB
Zagreb, Croatia
Summary
🤩
Rockstar🎓
Top SchoolMarko Topolnik is a senior software engineer with over two decades of low-level systems experience and a recent focus on Rust-driven real-time and batch data processing. He designed and implemented core subsystems at Hazelcast—including a log-structured Hot Restart persistence layer and a coroutine-based Jet execution engine delivering billion-event-per-second throughput—and later built from scratch a Tokio-powered distributed operator DAG with queriable state. At QuestDB and in open-source contributions he’s driven bug fixes and SQL/engine optimizations, while at tvbeat he achieved a 6x batch performance improvement and cut memory complexity via streaming redesigns. Comfortable across Java, Rust, and Go, he blends deep performance tuning, systems design and practical product discovery, and has a track record of turning research-grade ideas into production-ready, highly parallel systems. An interesting throughline: he repeatedly rethinks storage and execution models to minimize IO and memory overhead, enabling millisecond-level latency at scale.
11 years of coding experience
25 years of employment as a software developer
PhD Computer Science, PhD Computer Science at FER
English, German
Stackoverflow
198,121reputation
16.8mreached
3,365answers
60questions
lucene
top-5%
synchronization
top-1%
arraylist
top-1%
maven
top-5%
regex
top-1%
dictionary
top-5%
Github Skills (128)
timeseries-database10
multithreading10
databases10
java-streams10
if-statement10
javas10
overriding10
abstract-class10
eclipse10
concurrency10
garbage-collection10
kotlin-coroutines10
enums10
stream10
parallel-processing10
Programming languages (14)
Github contributions (5)
hazelcast/hazelcast
Jul 2015 - Mar 2021
Hazelcast is a unified real-time data platform combining stream processing with a fast data store, allowing customers to act instantly on data-in-motion for real-time insights.
Role in this project:
Back-end Developer
Back-end DeveloperContributions:7 reviews, 683 commits, 153 PRs in 5 years 9 months
Contributions summary:Marko primarily focused on refactoring and cleaning up code, specifically within the Hazelcast Jet core module. They were involved in optimizing the concurrent queue implementation, enhancing the performance and reliability of the job execution. Their work included code style improvements, Javadoc updates, and changes to the API.
computationstream-processingbigtablereal-timestreaming-data
gunnarmorling/1brc
Jan 2024 - Feb 2024
1️⃣🐝🏎️ The One Billion Row Challenge -- A fun exploration of how quickly 1B rows from a text file can be aggregated with Java
Role in this project:Back-end Developer
Back-end DeveloperContributions:9 reviews, 4 PRs, 34 comments in 1 month
Contributions summary:Marko primarily contributed to the development of a Java-based application within the context of the One Billion Row Challenge. Their work focused on generating measurement data with randomized station names, optimizing name generation, and integrating a SWAR-based temperature parsing mechanism. The commits reflect an iterative process of performance improvement, including the introduction of techniques like unsafe memory access and optimized hashing. The user's contributions demonstrate a strong focus on optimizing Java code for high-performance data processing.
1brc
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