Off By OnePostmortems, tutorials and explainers on Postgres, Node, Go, testing and reliability. Real code, real EXPLAIN output, written by four developers.https://sitemoment.com/demo/minimal-off-by-one/enA boring monorepo layout that has survived three years and 40 packageshttps://sitemoment.com/demo/minimal-off-by-one/posts/pragmatic-monorepo-layout/https://sitemoment.com/demo/minimal-off-by-one/posts/pragmatic-monorepo-layout/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.Wed, 28 Oct 2026 00:00:00 GMTToolingNode.jsHana SatoHow to read a flame graph without guessinghttps://sitemoment.com/demo/minimal-off-by-one/posts/reading-flame-graphs/https://sitemoment.com/demo/minimal-off-by-one/posts/reading-flame-graphs/Width is time, height is call depth, colour means nothing. A practical guide to reading CPU flame graphs from Go's pprof, using a real regression we fixed.Wed, 14 Oct 2026 00:00:00 GMTPerformanceGoMarek DvořákRenaming a column without downtime: expand, migrate, contracthttps://sitemoment.com/demo/minimal-off-by-one/posts/zero-downtime-column-renames/https://sitemoment.com/demo/minimal-off-by-one/posts/zero-downtime-column-renames/ALTER TABLE ... RENAME COLUMN takes a millisecond and breaks every running pod. A step-by-step expand and contract rename in Postgres, with the trigger we use.Wed, 30 Sep 2026 00:00:00 GMTPostgresReliabilityIlse BrandtTIL: our trial countdown was wrong one day a year, and only in Europehttps://sitemoment.com/demo/minimal-off-by-one/posts/testing-time-dependent-code/https://sitemoment.com/demo/minimal-off-by-one/posts/testing-time-dependent-code/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.Wed, 09 Sep 2026 00:00:00 GMTTestingNode.jsHana SatoFeature flags without a vendor: one table, one function, one rulehttps://sitemoment.com/demo/minimal-off-by-one/posts/feature-flags-without-a-vendor/https://sitemoment.com/demo/minimal-off-by-one/posts/feature-flags-without-a-vendor/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.Wed, 05 Aug 2026 00:00:00 GMTToolingPostgresHana Sato40 MB an hour: the Node memory leak hiding behind setMaxListeners(0)https://sitemoment.com/demo/minimal-off-by-one/posts/node-memory-leak-event-listeners/https://sitemoment.com/demo/minimal-off-by-one/posts/node-memory-leak-event-listeners/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.Tue, 21 Jul 2026 00:00:00 GMTNode.jsPerformanceTobi OkekeThe index that did nothing: reading an EXPLAIN plan line by linehttps://sitemoment.com/demo/minimal-off-by-one/posts/the-index-that-did-nothing/https://sitemoment.com/demo/minimal-off-by-one/posts/the-index-that-did-nothing/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.Wed, 03 Jun 2026 00:00:00 GMTPostgresPerformanceIlse BrandtA retry helper with full jitter, in about 40 lines of Gohttps://sitemoment.com/demo/minimal-off-by-one/posts/retry-helper-with-jitter/https://sitemoment.com/demo/minimal-off-by-one/posts/retry-helper-with-jitter/Exponential backoff without jitter turns one outage into synchronized waves of retries. Here is a small Go helper that gets backoff, jitter and cancellation right.Wed, 27 May 2026 00:00:00 GMTGoReliabilityTestingMarek DvořákIdempotency keys for webhooks: the ten lines that stop double chargeshttps://sitemoment.com/demo/minimal-off-by-one/posts/webhook-idempotency-keys/https://sitemoment.com/demo/minimal-off-by-one/posts/webhook-idempotency-keys/Webhook providers deliver at least once, so your handler will see duplicates. A unique key and one transaction in Postgres make that harmless.Tue, 12 May 2026 00:00:00 GMTReliabilityPostgresIlse Brandt