NKESSLING@TERMINALSCREEN NOTEOpen to work from Nov 2026RTM 23:02:08 · UTC 21:02

NOTE ~/writing BUILD SYSTEMS

30 August 20269 min readby Noa Kessling

Cache keys are inputs, not branch names

How hashing a step's real inputs took median CI from 18 minutes to 3.

NOTE · PLAIN TEXT

How hashing a step's real inputs took median CI from 18 minutes to 3.

If your cache key contains the branch name, every new branch starts cold. The only honest key is a hash of what the step reads.

What counts as an input

Source files, environment variables the step reads, and the toolchain version. Forgetting the toolchain cost us a week of confusing hits after an upgrade.

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NOTE WRITING · RESEARCH NOTES8 NOTES

Keep reading.

Short write-ups of things that broke and how they got fixed. Plain language, real numbers.

Storage

18 SEPT 20267 min READ

You also have to fsync the directory

Why a new file is not durable until its directory is, and the crash test that proved it.

READ NOTE <GO>

30 AUG 2026Build systemsCache keys are inputs, not branch names9 min 12 JUL 2026DatabasesFair queues in Postgres, with SKIP LOCKED11 min 02 JUN 2026StorageGroup commit, drawn by hand6 min 09 MAY 2026ToolingBenchmarks that fail the build8 min ALL NOTES ↗

SCRN WORK · SCREENER6 OF 8 SHOWN

The projects behind the notes.

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ROLEKEY RESULT

TIDEA write-ahead log that survives the power cordtidewaterAuthor · maintainerRust2024–264,8121.92 GB/s append, one core KILNA build cache that made CI six times fasterkilnAuthorGo2023–262,2076.1x faster CI, median LOOMA Postgres job queue that stays fair under loadloom-queueAuthor · 3 contributorsTypeScript2024–251,39012k/s jobs on one node WRENRelease notes that write themselves from commitswrenAuthorTypeScript2025–261,04511 min saved per release PRSMRead traces in the terminal and diff two runsprism-traceAuthorRust2025961O(n log n) trace diff, was O(n²)FERNA small config language with typesfernAuthorZig2025–266120.4 ms compile a 2k-line config

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