Engineering consultancy specializing in fintech, banking, payments, and travel. We track down the problems other consultants gave up on.https://grupavii.eu/en-ushttps://grupavii.eu/blog/deep-tracks-mapping-india-outside-the-heap/https://grupavii.eu/blog/deep-tracks-mapping-india-outside-the-heap/When your dataset is 33 billion grid squares and your deployment constraint is one machine, the JVM's garbage collector becomes your enemy. How memory-mapped files turned an impossible memory problem into a solved one.Thu, 24 Sep 2026 00:00:00 GMTJVMPerformanceMemory ManagementDeep Trackscontact@grupavii.eu (Szymon Kaczorowski)https://grupavii.eu/blog/the-overgrown-trail/https://grupavii.eu/blog/the-overgrown-trail/A healthcare financial system's batch processing took an hour. After the rewrite, it took 45 seconds. But the 80x speedup wasn't the real win was removing the production risks that had accumulated over years of neglect.Tue, 17 Mar 2026 00:00:00 GMTLegacyPerformanceHealthcareFrom the Fieldcontact@grupavii.eu (Szymon Kaczorowski)https://grupavii.eu/blog/picking-up-the-scent/https://grupavii.eu/blog/picking-up-the-scent/A CTO asked for an honest assessment of their stack before a board presentation. What I found in two days changed how she talked about engineering to her board, and probably saved the company from a painful surprise during their next fundraise.Thu, 26 Feb 2026 00:00:00 GMTDue DiligenceArchitectureStrategyFrom the Fieldcontact@grupavii.eu (Szymon Kaczorowski)https://grupavii.eu/blog/the-stampede/https://grupavii.eu/blog/the-stampede/The program had forty engineers and was shipping slower than when it had five. A story about the paradox of scaling engineering teams, and why the fix was organizational, not technical.Sat, 14 Feb 2026 00:00:00 GMTScalingTeamsGrowthFrom the Fieldcontact@grupavii.eu (Szymon Kaczorowski)https://grupavii.eu/blog/old-growth-new-trails/https://grupavii.eu/blog/old-growth-new-trails/Building foundations for a mainframe migration that processes a million transactions per minute. How golden paths, quality standards, and the right frameworks let you scale beyond your own team.Wed, 22 Jan 2025 00:00:00 GMTMainframeMigrationArchitectureFrom the Fieldcontact@grupavii.eu (Szymon Kaczorowski)https://grupavii.eu/blog/the-trail-that-went-cold/https://grupavii.eu/blog/the-trail-that-went-cold/When peer-to-peer RSocket communication suddenly stops working, the logs show nothing. The docs say everything should work. Sometimes the only trail left is the source code itself.Wed, 15 Jan 2025 00:00:00 GMTRSocketDebuggingMicroservicesOn the Trailcontact@grupavii.eu (Szymon Kaczorowski)https://grupavii.eu/blog/lost-in-a-forest-you-built/https://grupavii.eu/blog/lost-in-a-forest-you-built/The architecture that worked at 10,000 users won't work at 100,000. Here are the warning signs that you're approaching a ceiling.Wed, 08 Jan 2025 00:00:00 GMTArchitectureScalingGrowthcontact@grupavii.eu (Szymon Kaczorowski)