# Kern Notes

> Systems Engineering Essays & Sunday Digest by Henrik Lindqvist (Stockholm, Sweden).

## Primary Sections
- [Home](https://template-kern-notes.flino.ai/)
- [All Essays](https://template-kern-notes.flino.ai/articles)
- [Topics Directory](https://template-kern-notes.flino.ai/topics)
- [Chronological Archive](https://template-kern-notes.flino.ai/archive)
- [Sunday Digest Subscription](https://template-kern-notes.flino.ai/subscribe)
- [Sponsorship Media Kit](https://template-kern-notes.flino.ai/sponsor)
- [About Henrik Lindqvist](https://template-kern-notes.flino.ai/about)
- [Contact & Errata Desk](https://template-kern-notes.flino.ai/contact)
- [Full-Text RSS Feed](https://template-kern-notes.flino.ai/rss.xml)

## Engineering Topics
- [Systems Architecture](https://template-kern-notes.flino.ai/topics/systems-architecture): Consensus quorums, ring-buffer backpressure, failure-domain isolation, and tail-latency budgets across multi-zone clusters.
- [Edge & Runtime](https://template-kern-notes.flino.ai/topics/edge-runtime): WebAssembly component cold starts, virtual memory copy-on-write snapshots, and regional request routing.
- [Storage Engines](https://template-kern-notes.flino.ai/topics/storage-engines): LSM compaction pacing, NVMe NAND die-plane interference, write-ahead log checkpoints, and page-cache mechanics.
- [Web Platform & A11y](https://template-kern-notes.flino.ai/topics/web-platform-a11y): Native HTML top-layer dialogs, CSS scroll containment, refreshable braille hardware testing, and zero-CLS rendering.
- [Observability](https://template-kern-notes.flino.ai/topics/observability): Per-CPU eBPF histograms, socket queue residency probes, hardware clock correlation, and sub-1% telemetry budgets.
- [Developer Tooling](https://template-kern-notes.flino.ai/topics/developer-tooling): Content-addressed monorepo build caches, deterministic archive digests, and reproducible CI pipelines.

## Published Essays
- [Deterministic Raft Lease Quorums Under Asymmetric Cross-AZ Jitter](https://template-kern-notes.flino.ai/articles/deterministic-raft-lease-quorums-under-asymmetric-jitter): Why leader read leases silently violate linearizability when NIC receive queues stall on one availability zone, and how monotonic hardware clock bounds eliminate split-read windows at p99.9.
- [Anatomy of a Sub-Millisecond WebAssembly Component Cold Start](https://template-kern-notes.flino.ai/articles/anatomy-of-a-sub-millisecond-wasm-component-cold-start): Breaking down every microsecond between TLS ALPN negotiation, `mmap` code-page faults, linear memory copy-on-write snapshots, and WASI Preview 2 host call trampolines.
- [Pacing LSM-Tree Compaction Debt on High-Queue NVMe Drives](https://template-kern-notes.flino.ai/articles/pacing-lsm-compaction-on-zoned-nvme-drives): Unthrottled background merges starve foreground point lookups long before disk bandwidth saturates. Here is a token-bucket scheduler keyed to device read-vs-write latency asymmetry.
- [Top-Layer HTML Dialogs and Tactile Braille Focus Discipline](https://template-kern-notes.flino.ai/articles/top-layer-dialogs-and-braille-display-focus-discipline): Replacing 14 kilobytes of custom JavaScript focus-trap listeners with native `<dialog>`, CSS `overscroll-behavior`, and live-region hygiene tested on physical 40-cell refreshable braille hardware.
- [Sub-1% Overhead Tail-Latency Histograms With Per-CPU eBPF Maps](https://template-kern-notes.flino.ai/articles/low-overhead-ebpf-tail-latency-histograms): Why user-space OpenTelemetry spans miss kernel socket-buffer queueing delays, and how log-linear BPF per-CPU arrays capture every microsecond stall at 420,000 requests per second.
- [Registered Buffer Rings in io_uring for High-Fanout RPC Gateways](https://template-kern-notes.flino.ai/articles/zero-copy-io-uring-framing-for-rpc-gateways): Replacing `epoll` readiness loops with kernel-managed multishot `IORING_OP_RECV` buffer rings cut syscall overhead by 71% on 100GbE internal service meshes.
- [Predictable SQLite WAL Checkpoints in Read-Heavy Edge Services](https://template-kern-notes.flino.ai/articles/predictable-sqlite-wal-checkpoints-in-read-heavy-services): Preventing unbounded `-wal` file growth caused by forgotten long-lived read transactions, plus exact `PRAGMA` settings for multi-gigabyte embedded catalogs.
- [Content-Addressed Monorepo Build Caches Without Silent CI Drift](https://template-kern-notes.flino.ai/articles/content-addressed-monorepo-caches-without-ci-drift): Why timestamps, unsorted directory globs, and leaked host `PATH` variables poison remote build caches—and a 120-line digest verifier that pushed our cache hit rate from 61% to 96.4%.