ZIO-LMDB

ZIO-LMDB is an embedded, ACID, key-value database for Scala applications built on ZIO.
It wraps lmdb-java with a higher-level, type-safe API that integrates naturally with the ZIO effect system.

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Why ZIO-LMDB?

• Zero infrastructure — the database lives in-process, no server to run or maintain.
• ACID guarantees — full transactional semantics backed by LMDB’s copy-on-write B+ tree.
• Type-safe API — keys and values are fully typed; codecs are resolved at compile time.
• ZIO-native — every operation returns a ZIO effect with precise error channels.
• Honest signatures — the return type tells you exactly what can go wrong.
• JSON storage by default — derives LMDBCodecJson is all you need; custom codecs are supported.
• Lexicographic ordering — keys are automatically sorted, enabling efficient range scans.

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Collection types

Type	Cardinality	Facade
Regular	one key → one value	LMDBCollection[K, T]
Multi	one key → many values	LMDBMulti[K, T]
Index	one key → many keys	LMDBIndex[FROM, TO]

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Quick install

Add the dependency to your build.sbt:

libraryDependencies += "fr.janalyse" %% "zio-lmdb" % "2.8.3"

For scala-cli scripts, add at the top of your file:

//> using dep fr.janalyse::zio-lmdb:2.8.3
//> using javaOpt --add-opens java.base/java.nio=ALL-UNNAMED --add-opens java.base/sun.nio.ch=ALL-UNNAMED

The JVM options are required when running on recent JVMs (Java 17+).

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Minimal example

import zio.*, zio.lmdb.*, zio.lmdb.json.*

case class User(name: String, age: Int) derives LMDBCodecJson

val program = for {
  users  <- LMDB.collectionCreate[String, User]("users", failIfExists = false)
  _      <- users.insert("alice", User("Alice", 30))
  result <- users.fetch("alice")
  _      <- Console.printLine(result)
} yield ()

object Main extends ZIOAppDefault:
  def run = program.provide(LMDB.liveWithDatabaseName("my-app"), Scope.default)

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JVM requirements

When LMDB is used with recent JVMs, add the following options at startup:

--add-opens java.base/java.nio=ALL-UNNAMED
--add-opens java.base/sun.nio.ch=ALL-UNNAMED

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In this documentation

• Getting Started — setup, layers, and your first CRUD operations.
• LMDBCollection — one key → one value collections.
• LMDBMulti — one key → many values collections.
• LMDBIndex — key-to-key index collections.
• Transactions — atomic multi-operation transactions.
• Codecs — key codecs and value codecs reference.
• Query DSL — fluent query and join API.
• Configuration — all configuration parameters.