whichdb
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LMDB vs UnQLite

LMDB: Tiny memory-mapped B+tree with ACID transactions and lock-free readers; reached 1.0 in 2026. UnQLite: Embedded, transactional key-value and JSON document engine in a single C file, with Jx9 scripting.

key differences

  • LMDB is built for larger datasets (≤ 10 TB) than UnQLite (≤ 100 GB).
  • Only UnQLite has json, in-memory, online schema changes.

choose lmdb for

  • +Read-heavy embedded indexes and caches
  • +Directory services (OpenLDAP back-mdb)
  • +Blockchain and wallet state
  • +ML dataset storage with fast random reads

best at · Embedded, Metadata, Local-first

choose unqlite for

  • +Embedded devices and firmware needing local storage
  • +Desktop or game apps storing JSON state
  • +Local caches inside native services

best at · Embedded, IoT, Coordination

LMDBTiny memory-mapped B+tree with ACID transactions and lock-free readers; reached 1.0 in 2026.
UnQLiteEmbedded, transactional key-value and JSON document engine in a single C file, with Jx9 scripting.
overview
Primary model
Key-Value
Key-Value
Also supports
–
Document
Type
Embedded library
Embedded library
Status
Active
Active
Developer
Symas Corporation / OpenLDAP Project
Symisc Systems
First release
2011
2013
Latest version
1.0.2 (Sep 8, 2026)
1.2.1 (May 1, 2026)
License
Open source (permissive)OpenLDAP Public License 2.8
Open source (permissive)BSD 2-Clause
Free tier
✓
✓
popularity
WhichDB Score
39.7
4.1
Rank
#47
#419
GitHub stars
3.1K
2.3K
Stack Overflow questions
260
–
scale & guarantees
Comfortable data size
Medium (≤ 10 TB)
Small (≤ 100 GB)
Horizontal scaling
None
None
Multi-region
None
None
ACID
Full
Full
Consistency
Strong
Strong
Schema
Schemaless
Schemaless
Architecture
Embedded
Embedded, In memory
deployment
Self-hosted
✓
✓
Vendor-managed cloud
—
—
Serverless
—
—
Embedded
✓
✓
Edge
—
—
Clouds
–
–
capabilities
Transactions
✓
✓
Joins
—
—
Secondary indexes
—
—
Full-text search
—
—
Vector search
—
—
Geospatial
—
—
JSON
—
✓
Change data capture
—
—
Triggers
—
—
Stored procedures
—
—
Materialized views
—
—
TTL / expiry
—
—
Pub/Sub
—
—
Columnar storage
—
—
In-memory
—
✓
Durable persistence
✓
✓
Compression
—
—
Encryption at rest
—
—
Role-based access
—
—
Time travel
—
—
Branching
—
—
Online schema changes
—
✓
Streaming ingest
—
—
Offline sync
—
—
Runs in WebAssembly
—
—
interfaces
Query languages
C API
Jx9, Key-value C API
Client languages
C, C++, Python, Go, Rust, Java, JavaScript
C, C++, Python
Best for
Embedded, Metadata, Local-first
Embedded, IoT, Coordination, Edge
Add more to this comparisonNot sure either fits? Try smart match

LMDB vs UnQLite: FAQ

What is the difference between LMDB and UnQLite?

LMDB: Tiny memory-mapped B+tree with ACID transactions and lock-free readers; reached 1.0 in 2026. UnQLite: Embedded, transactional key-value and JSON document engine in a single C file, with Jx9 scripting. LMDB is built for larger datasets (≤ 10 TB) than UnQLite (≤ 100 GB). Only UnQLite has json, in-memory, online schema changes.

When should I choose LMDB over UnQLite?

Choose LMDB for read-heavy embedded indexes and caches; directory services (OpenLDAP back-mdb); and blockchain and wallet state. Choose UnQLite for embedded devices and firmware needing local storage; desktop or game apps storing JSON state; and local caches inside native services.

Is LMDB or UnQLite more popular?

LMDB ranks #47 on the WhichDB Score (39.7/100) and UnQLite ranks #419 (4.1/100). Popularity is not fit: check the requirements that matter for your project.

Are LMDB and UnQLite open source?

Yes. LMDB is open source. License: OpenLDAP Public License 2.8. Yes. UnQLite is open source. License: BSD 2-Clause.