package lmdb

  1. Overview
  2. Docs

High level bindings for LMDB.

The LMDB database is a fast in-file key-value store that supports ACID transactions.

These bindings attempt to expose a typesafe yet low-overhead API.

First, an environment must be opened using Env.create:

let env = Env.(create Rw ~flags:Flags.no_subdir "mydb")

Now the data file mydb and lock file mydb-lock have been created in the current directory.

One environment may contain multiple named and one unnamed key-value stores. They are called databases in the LMDB documentation, but called maps in these OCaml bindings.

A single ('key, 'value, [< `Read | `Write], [< `Dup | `Uni ]) Map.t is a key-value store mapping OCaml values of type 'key to values of type 'value. Multiple values per key are supported on request.

Using Map, we can open the unnamed map and add our first value:

let map = Map.open_existing Nodup ~key:Conv.string ~value:Conv.string env in
Map.add map "Bactrian camel" "Elegant and beautiful animal with two humps."

Transactions and Iterators are also available.

Raw bindings

module Mdb : sig ... end

Raw bindings for LMDB.

Permissions

type 'a perm =
  1. | Ro : [ `Read ] perm
  2. | Rw : [ `Read | `Write ] perm

This library uses [< `Read | `Write ] phantom types to encode the read/write permissions of transactions and cursors. The following values are used to request read-only or read-write permissions on environments, transactions and cursors.

Database

module Env : sig ... end

Collection of maps stored in a single memory-mapped file.

module Txn : sig ... end

Series of operations on an environment performed atomically.

module Conv : sig ... end

Converters to and from the internal representation of keys and values. A converter contains serialising and deserialising functions as well as the flags applied when the converter is used in a map.

module Map : sig ... end

Key-value maps.

module Cursor : sig ... end

Iterators over maps.

Error reporting

exception Exists

Raised when adding an already existing key to a `Uni map or adding an an already existing value with Map.Flags.no_dup_data to a key of a `Dup map.

Also raised when trying to add ~flags:Flags.append(_dup) non-sorted data.

exception Not_found

Raised when searching for non-existing key

exception Map_full

Raised when memory map is full

exception Error of int

Other errors are reported with Invalid_arg s or Error n.

val pp_error : Stdlib.Format.formatter -> int -> unit

pp_error Format.std_formatter e prepares a human-readable description of the given error code n raised via Error n.

val version : string * int * int * int

(name, major, minor, patch)