Caveman Skill: Token-Efficient AI Response Protocol

role: backend engineer, domain: distributed systems, max_length: 300, task: Why is my Redis Pub/Sub losing messages under high load and how do I fix it?

**Root cause:** Redis Pub/Sub is fire-and-forget — no persistence, no acknowledgment, no replay. Under high load, slow subscribers get dropped messages because Redis doesn't buffer for them. **Fix options ranked by reliability:** 1. **Switch to Redis Streams** (recommended) - `XADD` to write, `XREADGROUP` for consumer groups with ACK - Survives subscriber restarts, supports replay - `XREAD COUNT 100 BLOCK 0 STREAMS mystream $` 2. **Add a queue layer** (if you need ordering guarantees) - Use BullMQ or Kafka in front of Redis - Redis Streams + consumer groups handles most cases without this 3. **Tune subscriber throughput** (stop-gap only) - Increase `client-output-buffer-limit pubsub` in redis.conf - Default: `256mb 64mb 60` — raise the soft limit - This delays drops, doesn't eliminate them **Verify message loss:** ```bash redis-cli INFO stats | grep rejected_connections redis-cli CLIENT LIST | grep omem ``` High `omem` on a subscriber = it's falling behind. Switch to Streams.