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~/tips/today — 2026-10-06

~cat tips/today

Sample traces at the tail, keep every error

observabilityopentelemetry

Head-based sampling at 10 percent throws away 90 percent of failures, because the coin is flipped before the request knows it's going to fail. Decide at the end instead: keep everything with an error or above p99, plus 2 percent of the rest by trace id.

tail_sampling:
  decision_wait: 30s
  policies: [status_code: ERROR, latency: 800ms, probabilistic: 2]

Set decision_wait longer than your slowest request, or the slow ones get dropped as "not slow yet".

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