When designing high-throughput in-memory caches, engineers face a tough choice between memory efficiency and CPU consumption. Passive key expiration guarantees memory leaks for cold keys that are never read again, while naive active sweeping introduces devastating latency spikes that degrade application performance.
The solution lies in an adaptive, randomized active reaper that samples a small subset of keys and loops recursively only when the ratio of expired keys exceeds a specific threshold, typically 25%. However, this means accepting a permanent memory overhead of up to 25% of expired, un-reclaimed keys to protect your critical tail latency.
Understanding how to tune these sweep frequencies and CPU time limits is essential for anyone building reliable, stateful services under heavy load.
Read the full article: Managing Cache Expiration Without CPU Spikes: Designing Adaptive TTL Reapers
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