# fjall-rs/fjall

🗻 Log-structured, embeddable key-value storage engine written in Rust

Repository: https://github.com/fjall-rs/fjall
Canonical: https://ross.abutalabs.com/products/fjall
Homepage: https://fjall-rs.github.io
Language: Rust
License: Apache-2.0
License Family: permissive
Topics: database, lsm, lsm-tree, lsmt, rust, rust-lang, storage-engine, embedded-database, embedded-kv, kv, kv-database, kv-storage, kv-store, log-structured, log-structured-merge-tree, key-value-database, key-value-store, embeddable, embeddable-database, key-value-storage
Last push: 2026-08-24T16:05:46+00:00

## Health v2 (maintenance only)
Score: 93/100 (v2, computed 2026-09-02T17:46:02.011165+00:00)
- activity 99, release rhythm 98, longevity 72
- inputs: {"age_days": 1021, "days_push": 9, "days_rel": 18, "gap_med": 5.5, "n_releases_24m": 53}
- flags: none
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 2291, forks 117 (observed 2026-08-28T04:06:34.953280+00:00)

## What it is
Fjall is a log-structured (LSM-tree-based), embeddable key-value storage engine written in 100% safe Rust, similar in spirit to RocksDB. It offers a thread-safe BTreeMap-like API with multiple keyspaces, range/prefix iteration, optional serializable transactions, built-in LZ4 compression, and key-value separation for large blobs.

## Use cases
- embed a key-value store in a Rust application
- replace RocksDB or LevelDB with a pure-Rust storage engine
- store large blobs with key-value separation
- build a database or index on top of an LSM-tree engine
- run range and prefix scans with forward and reverse iteration
- use column-family-like keyspaces with atomic cross-keyspace writes
- need serializable transactions in an embedded store

## When to choose
- you need an embeddable, serverless key-value engine in Rust
- you want RocksDB-like LSM performance without C++ dependencies
- you need multiple keyspaces, transactions, or blob separation in-process

## When to avoid
- you need a standalone database server or network API
- you need a relational database, SQL, or query language
- your project is not in Rust

## Facets
- artifact type: library
- maturity: active
- function: database, serialization, caching
- domain: databases, developer-tools, backend
- platform: rust, cross-platform
- tags: lsm-tree, key-value-store, embedded-database, storage-engine, keyspace, transactions, compression

## Member repositories
- fjall-rs/fjall (main) score 93

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:06:34.953280+00:00.
- Health v2: computed from the inputs above; adoption is never an input.
- Inferred fields (summary, facets, guidance): AI-extracted, prompt v1, taxonomy v1, on 2026-08-30T02:40:40.689720+00:00, confidence not recorded.
  - readme: https://github.com/fjall-rs/fjall (fetched 2026-08-28T04:06:34.953280+00:00, sha a39f76e9dbfe)
  - homepage: https://fjall-rs.github.io (fetched 2026-08-29T10:20:52.353976+00:00, sha 6869644eb5c9)
  - registry_crates: https://crates.io/api/v1/crates/fjall (fetched 2026-08-29T10:20:52.363026+00:00, sha 643fe52a2695)
- Data as of 2026-08-30T08:39:29.467469+00:00.