[jandrewrogers]

Many databases ordinarily modify the page cache 10 million times per second under load. I have one doing that right now on an i3en.12xlarge, which is only half a server. Not every cache replacement algorithm family has that kind of throughput but some common algorithm families do e.g. clock-sweep variants.

The "high-probability" refers to a type of pattern, not a specific instance, so there is no implication of recency. A page access pattern can be detected frequently but involve different pages each time.

Bélády's optimality theorem means cache replacement algorithm performance is governed by the theoretical limits on sequence prediction. You can optimize for either breadth or depth; improving performance for one pattern necessarily reduces performance for others. In practice, database caches optimize heavily for a few patterns and ignore the rest; the performance for the patterns they ignore is not much worse than if they optimized for all patterns equally, so it is a good trade.