I'm sure it's been done before, but right now I feel smart about the recognition.
I want to make postgres' buffer cache take into account whether previous accesses where synchronous or asynchronous:
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I.e. tag pages that needed to be read in synchronously with that fact (or reversely ones that were prefetchable).
That's somewhat similar to the old idea of (IIRC) to just always keep inner index pages around more aggressively.
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It actually targeted all index pages - there are so few internal pages that they're bound to stay in buffer cache without any help. pgbench_accounts pkey pages are ~6x more popular than heap pages -- big disparity is normal. That should be represented, somehow.