Prep RoomSign inStart free
Code RoomLSM compaction space amplification
HardPrep Room Coding #3156

LSM compaction space amplification

System designDistributed systemsSenior–Staff~45 min

An LSM-based key-value store backing a metadata service is suffering: disk usage is 2.3x the live dataset, read p99 has crept to 40ms, and deletes don't seem to free space for days. Workload is heavy overwrites of the same keys (config/state that updates frequently) plus a steady stream of deletes (TTL expiry), uniform key distribution, dataset ~3TB. Design a compaction strategy (and the surrounding knobs) to fix space amplification, restore read latency, and make deletes reclaim space promptly. Explain the trade-offs versus the alternative strategy.

What a strong answer looks like

Clarify scale and constraints first. Propose a clean component breakdown, then go deep on the hard parts (data model, bottlenecks, consistency, failure modes) and name the trade-offs you are making.

Clarify5:00 left
Estimate5:00 planned
Design15:00 planned
Deep dive12:00 planned
Failure8:00 planned
0:00
Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.