Gregory Ssiyankai
Switzerland
Summary
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RockstarGregory Ssiyankai is a seasoned software engineer based in Switzerland with 12 years of experience specializing in big data, network security, and backend systems. He combines deep low-level optimization skills with rigorous test automation, evidenced by contributions to high-performance Java bitset projects like RoaringBitmap and javaewah. His work includes implementing core iterators, fixing iterator bugs, adding comprehensive unit tests, and creating JMH benchmarks to measurably improve performance in real-world libraries used by Apache Spark and other major systems. Gregory favors pragmatic refactoring to remove duplication and sharpen index lookups, balancing maintainability with throughput gains. Comfortable across the performance stack, he brings a track record of shipping reliable, well-tested improvements that matter in large-scale data platforms. An often-overlooked strength is his ability to translate micro-optimizations into measurable system-level benefits through disciplined benchmarking.
12 years of coding experience
Chinese, German, French, English
Github Skills (17)
algorithm10
unit-testing10
algorithms10
bitmap10
performance-analytics10
performance-monitor10
roarr10
data-structure10
java10
performance-measurement10
bitset10
javas10
performance-analysis10
performance-tuning10
data-structures10
Programming languages (6)
Github contributions (5)
lemire/javaewah
Mar 2014 - Mar 2016
A compressed alternative to the Java BitSet class
Role in this project:
Back-end Developer & Test Automation Engineer
Back-end Developer & Test Automation EngineerContributions:70 commits, 1 PR, 21 pushes in 2 years 1 month
Contributions summary:Gregory primarily focused on enhancing the functionality of a compressed alternative to the Java BitSet class, evidenced by the implementation of a clear int iterator and the addition of test cases. The user added the clear int iterator, a core feature for the bitset functionality. The user's contributions involved implementing a 32-bit version and addressing bugs related to the iterator. They developed unit tests to ensure the correctness of these implementations.
bitsetjavacompressedbitmap-indexesewah
RoaringBitmap/RoaringBitmap
Mar 2015 - Apr 2017
A better compressed bitset in Java: used by Apache Spark, Netflix Atlas, Apache Pinot, Tablesaw, and many others
Role in this project:Back-end Developer & Performance Engineer
Back-end Developer & Performance EngineerContributions:144 commits, 13 PRs, 116 pushes in 2 years
Contributions summary:Gregory's contributions primarily focus on performance optimization and benchmarking of a Java library for compressed bitsets. They implemented JMH benchmarks to measure the performance of core operations like "and". The code changes included optimizations to existing "and" operations and modifications to improve performance, with additional work on supporting worst-case scenario benchmarking. They also refactored the index lookup and removed duplicated code.
bigdataroaring-bitmapsspark-mlroaringbitmapdruid
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