2Q
Two queues (simplified)
Teaching 2Q: first touch → A1in (FIFO); re-hit while resident → Am (LRU). Paper 2Q (Johnson & Shasha) also keeps an A1out ghost list and promotes on ghost hit, not only on a second in-cache touch.
IdleStep a query
Simplified 2Q: first touch → A1in (FIFO, max ~2). Resident re-hit → Am. (Paper 2Q also has A1out ghosts.)
hits 0 · misses 0 · Space / ← →
2Q Cache Replacement