Master LMDB with lmcmd: A Powerful Command-Line Client

What is LMDB?

LMDB (Lightning Memory‑Mapped Database) is a high‑performance key‑value store that uses memory‑mapped files. It provides fast read/write access, strong multi‑version concurrency control (MVCC), and full ACID guarantees while storing all data in a single file.

Efficiency : Direct memory‑mapped file access eliminates extra copying.

Strong transactionality : MVCC ensures consistent reads during concurrent writes.

Lightweight : Single‑file storage makes it suitable for embedded systems and large‑scale deployments.

ACID guarantees : Atomicity, consistency, isolation, and durability are enforced.

Why lmcmd was created

LMDB stores data in a binary format, which makes manual inspection and debugging difficult. No dedicated command‑line management tool existed, so the author implemented lmcmd, a Python‑based interactive console inspired by redis-cli. It offers basic key‑value operations, import/export, and search capabilities for LMDB databases.

Installation

lmcmd is distributed on PyPI. Install it with one of the following commands:

pip install lmcmd

pip3 install lmcmd

Usage

Connecting to a database

Provide the path to the LMDB environment directory. If the directory does not exist, lmcmd creates a new environment.

lmcmd my_database

lmcmd /absolute/path/to/my_database

After a successful connection the interactive prompt appears.

Command reference

show

: Prints the name of the currently opened database. set <KEY> <VALUE>: Stores a key‑value pair. get <KEY>: Retrieves the value associated with <KEY>. del <KEY>: Removes the specified key. list: Lists all key‑value pairs in the environment. export: Writes the entire database to export.json in JSON format. import <ID> <FILE_PATH>: Loads key‑value pairs from a JSON file. search <VALUE>: Returns keys whose values contain the given substring.

Example session

>>> set name Alice
Ok
>>> get name
Alice
>>> list
{name: Alice}
>>> export
Data Exported to export.json
>>> import id data.json
Data Imported!
>>> show
Database: my_database
>>> del name
Ok
>>> list
(Empty)
>>> search Alice
{name: Alice}

Source code

GitHub repository: https://github.com/nodcats/lmcmd