I killed an in-memory database primary on purpose — fifteen times, across three down-after-milliseconds settings and three engines (Redis 8, Valkey 8, Dragonfly) — and timed how long writes actually fail before a replica takes over. Short answer: **your failover window is roughly down-after plus about two seconds of election and promotion — and it's the same no matter which engine is dying. * Here's the runnable lab, the numbers, and the traps that bite in production.* The ans...