Moving Less Bytes in Valkey: How One Optimization Broke Two Subsystems and What We Did About It

Valkey 9.0 shipped Reply Copy Avoidance - feature to reduce expensive data copies with lightweight references when sending replies to clients. Copy less, go faster. Simple idea. But why our benchmarks went up and after harmless fix in other subsystem we get -30% RPS? Investigating this took days of debugging and here are the answers!