Every night a batch job reads each of millions of keys once, and the next morning the cache hit rate has collapsed. Which eviction policy would have resisted that?

Options

• ✗ LRU: evict the least recently used key
• ✓ LFU: evict the least frequently used key Correct
• ✗ FIFO: evict the oldest inserted key
• ✗ Random: evict a randomly chosen key

Why

Under LRU the scan makes every one-off key "recently used", pushing out the keys real users ask for all day. LFU keeps the keys with many hits, so keys touched once are evicted first.

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