Idempotency keys for webhooks: the ten lines that stop double charges
Webhook providers deliver at least once, so your handler will see duplicates. A unique key and one transaction in Postgres make that harmless.
Issue 41 · Oct 2026October 28, 20269 stories · 7 topics
Plain text, monospace and hard-won lessons
A group blog in the old style: no tracking pixels, a full-text RSS feed, and posts long enough to include the actual code. Est. 2026, still typing in a terminal.
In brief
A boring monorepo layout that has survived three years and 40 packages
Three top-level folders, one dependency rule and pnpm filters for CI. The monorepo structure we keep coming back to, and what we stopped doing.
Start here
Node.js40 MB an hour: the Node memory leak hiding behind setMaxListeners(0)
A postmortem of a slow leak in a Node ingest service: how two heap snapshots, one retainer chain and a silenced warning led us to the bug.
Latest posts
Testing
TIL: our trial countdown was wrong one day a year, and only in Europe
A date test that passed for months failed on a CI runner in Berlin. What we learned about DST, local midnight and testing code that reads the clock.
Tooling
Feature flags without a vendor: one table, one function, one rule
For most teams, feature flags are a Postgres table, a hashing function and a policy about expiry dates. Here is ours, and when we would pay for a product instead.
Postgres
The index that did nothing: reading an EXPLAIN plan line by line
We added an index to fix a 1.2 second query and the plan did not change. Here is how EXPLAIN ANALYZE told us why, and the partial index that worked.
Browse by topic
- 01PostgresIndexes, query plans, migrations and the locks behind them, written from the point of view of the team that owns the database.4 stories
- 02Node.jsThe Node runtime in production: memory, the event loop, testing and the tooling around TypeScript services.3 stories
- 03GoGo services and workers: profiling with pprof, concurrency, retries and small helpers worth copying.2 stories
- 04ReliabilityRetries, idempotency, safe deploys and the habits that keep a service up when its dependencies are not.3 stories
- 05PerformanceFinding where the time and memory go, with measurements first and opinions second.3 stories
- 06TestingTests that catch real bugs: time, randomness, failure paths and the cases that only break in production.2 stories
- 07ToolingMonorepos, CI, feature flags and the internal tools a team builds instead of buying.2 stories