I'm having a hard time understanding why this is better than CLOCK. It seems like a hack to make updates easier which however makes both practical performance a

I'm having a hard time understanding why this is better than CLOCK. It seems like a hack to make updates easier which however makes both practical performance and conceptual justification much worse. The elements which are between 'hand' and 'tail' are going to stay there for a long time, until the hand pointer cycles. If there are lots of elements which get put in the cache but don't really deserve it, that could take a long time. But that's exactly the case where you wouldn't want to keep the elements behind the hand around for a long time. Remember, they got 'promoted' for appearing twice in around the cache size records. Not a great indication that they should be kept for a long time. On the other hand, when the pointer cycles, they could get thrown away quite easily. On the other hand CLOCK converges to a situation where elements which have appeared a lot are at the front. They are much less likely to be thrown out even if they have a temporary run of scarcity. The elements which don't appear much quickly bubble to the back and become much more likely to be thrown out in the next few evictions. This is accentuated if there are lots of elements which are getting hit relatively more frequently. After a long time of running SIEVE, there's not really anything about the state which will improve future performance compared to when it starts cold. In many cases it seems it will be locked in to a suboptimal state by overadapting to past observations.