medium Drill: cache size for a hot-key store
Drill
A key-value store holds 1 billion items, ~500 bytes each. ~10% are hot. Redis overhead ~40%. Size the cache and decide if it fits one node.
✅ Worked solution & bounds check
Worked solution
- Working set = 0.10 × 10⁹ × 500 B = 50 GB.
- × 1.4 overhead ≈ ~70 GB.
Gate: ~70 GB fits a single large Redis node (e.g. 128 GB RAM) — but you’re near the ceiling, so plan to shard (consistent hashing) before the hot fraction grows past ~200 GB.
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