A developer's field notes
Dev notes
Tech I went back and forth on, problems that only showed up once it shipped. Notes I keep so I don't forget.
💡 Today's Dev Insight
The size of a join result is determined not by table row counts but by the duplication of the join key. Overlapping 1:N chains makes intermediate results balloon multiplicatively, spilling past memory to disk, and when the estimated row count in an execution plan diverges sharply from the actual count, that's a sign of stale statistics.
In the Next.js App Router, a single 'use client' line that draws the server-client boundary reshapes your entire bundle size, data fetching, and state management strategy. Draw that boundary wrong and bundle bloat plus duplicate fetching blow up all at once, late in the game. This memo lays out the judgment principles for redrawing the boundary based on per-layer responsibilities and data ownership, plus the priority order for refactoring boundaries that were already drawn wrong.
Webhook receivers must be designed with distrust of external requests. Since requests can be unstable — with retries, processing delays, and even forgery attempts — signature verification, idempotent processing, retry ID tracking, and queuing for delays are all essential for stable ingestion. Particularly, retries arriving without idempotency keys lead to duplicate processing; when delays grow too long, immediately switch to queue locking.
Dependency caches, build caches, and matrix strategies cut CI runtime in half, but when invalidation criteria are set wrong, stale packages sail through builds and turn into unexpected incidents. This article walks through concrete situations where a cache actually breaks a build, and lays out principles for reading invalidation points correctly in lock files, hash inputs, and matrix key design, so you have a safe standard for using caches.
Even with an index in place, seeing a full scan in EXPLAIN is common. Four patterns sever the link between a query and its index: function-wrapped columns, type mismatches, leading wildcards in LIKE, and low selectivity. This post is a decision memo that walks through each pattern with real examples of how it distorts the execution plan, and lays out a procedure for narrowing down and fixing the cause, from reading EXPLAIN to confirming the root cause.
Korean web fonts carry large per-glyph payloads that delay loading, and the later a font arrives, the worse the CLS metric swings. This article walks through subsetting glyphs, nailing down preload timing, and choosing a font-display strategy with real numbers. It separates what Next.js's next/font handles from what it doesn't, and shows how to design a font pipeline that keeps text rendering stable without blowing the performance budget.
Suddenly enabling `strict` in a loosely-typed TypeScript project makes hundreds of errors pour out overnight. This article is a real migration log about enabling strict-family options one by one amid new feature development and bug fixes, weighing the difficulty and effect of each option to work out an optimal ordering. It covers everything from the `any` cleanup order to `strictNullChecks` and `noImplicitAny`, along with the real-world outages and regressions encountered along the way.
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