When Does CLOCK Choose Wrong?

Comparing original CLOCK (no decay) to sharded Bélády, by frequency of evicted item

Correct (matches Bélády) Wrong (Bélády chose differently)
Eviction Accuracy by Frequency
freq ≤ 2 accuracy
~50%
More right than wrong at lower freq
freq > 2 accuracy
~20%
Usually wrong to evict these!
The insight: Evicting high-frequency items is almost always wrong. If you can't make the right decision, don't make any decision — protect them instead.

Note: This demo uses a smaller trace/cache than the actual research, but still illustrates the pattern.