= Buffer cache eviction
Removing a <buffer cache key>'s resident contents so the storage in <computer memory> can serve another key. An unreferenced <clean buffer> can be reused directly in the <buffer cache state model>; an unreferenced <dirty buffer> requires successful <buffer cache writeback> first. A <pinned buffer> cannot be chosen regardless of cleanliness. <LRU replacement> ranks eligible candidates; it does not override lifetime protection. If every candidate is retained, a <cache miss> cannot obtain space until something releases a reference or capacity changes. This is a resource shortage, not permission to discard live contents.
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