Scan-resistant cache eviction

Your in-memory cache (fixed 64GB) is showing a low hit rate even though the popular working set easily fits in memory. Investigation shows occasional large scans (a batch job, a crawler) pull in thousands of one-hit-wonder keys that evict the genuinely hot keys under plain LRU, cache pollution. Design an eviction/admission policy that resists scan pollution, keeps the genuinely hot working set resident, and adapts as the popularity distribution shifts over time. Discuss how you'd measure that it's working.