Notes on making things faster

The blog.

Field notes from real optimization work — what I measured, what I changed, and what surprised me. Mostly builds, hot paths, and the profiler.

FeaturedJul 29, 2026 · 6 min read

parallel-zip 1.4.0: 26× faster — and here's exactly what that costs

The new default skips re-compressing anything it recognizes as already compressed, instead of sampling and guessing. It's a big speed win — and a real size cost I'm not going to hide from you.

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02The fastest way to compress a file is to not compress itA fat JAR build spends most of its CPU decompressing files and compressing them back into... the exact same bytes. Here is the ZIP-format trick shaded-jar uses to skip that work entirely — explained with moving boxes.Jul 19 · 5 min 03Slow shaded and fat JARsAfter parallel-zip, my next target: the slow building of fat and shaded JARs. Why this niche is worth years of my evenings, whether anyone will actually use it, and a first look at what the Shadow plugin leaves on the table.Jul 9 · 3 min 04Improving build of open source projects Part #2 - fixing the zip taskOne CPU core, zipping alone, eating a third of the build. Time to fix that — and make sure the fix doesn't backfire on the other ten projects.Jul 6 · 7 min 05Improving build of open source projects Part #1 - profilingWhat does a real contributor's CI actually run before tests even start? I pulled the exact commands from GitHub Actions and profiled them, two different ways, on three open-source projects.Jun 30 · 8 min