Design your LSM — and feel its trades

Every LSM knob — memtable size, level multiplier, leveled vs tiered, bloom bits-per-key, block size, compression — is a deliberate move on the same write-amp / read-amp / space-amp triangle, and the right configuration is dictated by the workload, not by a default.

Previously

All ten knobs are on the table. The capstone asks: given a workload, which ones do you turn — and which scene's insight justifies each turn?

Scene 11

Design your LSM — and feel its trades

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What to watch for

OLTP mixed: 10M keys × 1KB values, p99 read <5ms, disk budget 2× live data. Default knobs are pre-loaded; the verifier traces each to its scene.

Implementation

Highlighted lines are the ones running in the diagram right now.

LSM design checklist

knob → workload axis → earlier scene

1memtable size       → recovery time vs flush frequency  (scenes 2, 3)
2compaction policy   → write-amp vs read/space-amp        (scene 8)
3level multiplier    → #levels vs per-compaction work     (scene 7)
4bloom bits/key      → miss-cost vs RAM                   (scene 5)
5block size          → point-read I/O vs compression      (scene 10)
6compression         → CPU vs disk bytes                  (scene 10)
7block_cache_size    → hot-working-set fits in RAM?       (scene 10)
8tombstone retention → safe deletion vs space             (scene 9)

When LSM is the wrong answer

scene 1 is still in scope

1# fat values, low key cardinality, all point reads
2#   → Bitcask wins (scene 1 contrast)
3# transactional multi-key OLTP
4#   → B-tree DB (Postgres, MySQL) — LSM compaction is a tax here
5# columnar OLAP
6#   → Parquet + columnar engine — LSM cannot beat sort-merge-with-pushdown
7# tiny dataset that fits in RAM
8#   → just use a hash table

Sources

Where this sits in Build an LSM-tree storage engine (LevelDB / RocksDB style)

Scene 11 of 11, in the Sharp edges act — Tombstones, blocks, and the canvas.. Capstone: pick a workload, set knobs, watch the verifier trace each choice back to the scene that taught it. The amp triangle is the load-bearing trade.

All 11 scenes in Build an LSM-tree storage engine (LevelDB / RocksDB style) · Every curriculum

Designs that use this

Dropbox / Google DriveChunking, dedup, sync, conflict resolution.

Built with Arqly

Every scene in Build an LSM-tree storage engine (LevelDB / RocksDB style) builds on the one before it.All 11 Build an LSM-tree storage engine (LevelDB / RocksDB style) scenes