LMDB Archiver

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LMDB Archiver is a C++17/Qt 6 desktop archive manager that integrates naturally with Windows Explorer. It uses the ACID transactions and memory-mapped I/O of LMDB (Lightning Memory-Mapped Database) as its storage layer, and stores files as raw bytes (optional gzip compression is self-describing through the key, not the value). No headers or wrappers — a pure schema that is byte-compatible with the LucioraEla source system and any standard LMDB tool.

Download the latest Windows installer (MSI) · User guide · Build instructions

Why LMDB?

LMDB is a small, fast embedded key-value database originally developed for the OpenLDAP project. This project vendors the LMDB_0.9.33 source from the official GitHub mirror and links it statically through CMake.

• Memory mapping and zero-copy reads: Leverages the operating system's virtual memory and buffer cache for efficient lookups without a separate application cache.
• Full ACID transactions with MVCC: Preserves the pre-commit state even when an archive update fails or is cancelled midway.
• Read-dominated concurrency: Multiple read transactions never block each other or a writer; writes are serialized to avoid deadlocks.
• Sorted B+tree store: Keys are kept sorted, which fits sequential traversal and prefix-path lookups over archive entries well.
• Small, low-maintenance C library: No separate server, log-based recovery process, or background compaction service is required.

LMDB itself is not a compression format. LMDB Archiver uses it as-is — the key is a UTF-8 path, the value is the raw file bytes. No magic, headers, or compression are added, so Python lmdb, C liblmdb, C#, or any standard LMDB tool can read and write the archive directly. See the LMDB technical overview and the OpenLDAP project for the underlying principles.

Key features

• Add files and entire directories to a single .lmdb archive
• Browse the tree, search, overwrite, delete, and extract selected or all entries of an existing archive
• Two-way drag and drop with Windows Explorer, paste copied files with Ctrl+V, and copy archive entries with Ctrl+C to paste into Explorer
• Double-click a .lmdb to open it, plus right-click menus for Extract here and Pack folder into an LMDB archive
• UTF-8 paths and path-traversal protection
• LMDB transactions for non-destructive updates
• Readability verification of every record, with archive checking in both the GUI and CLI
• Atomic archive compaction that reclaims empty LMDB pages after deletion
• Byte-level compatibility with LucioraEla and all standard LMDB tools — read and write archives without this program
• Optional gzip compression — store compressed with standard gzip on add (self-describing .<hash>.gz key marker). Extraction auto-decompresses by default; you can also gunzip the file by hand
• Targets Qt 6.2 and above, with local builds verified on Qt 6.11/MSVC 2022 and CI set up for Windows/Linux/macOS

Full portability: the key is a UTF-8 path string and the value is the raw file bytes. With no magic, headers, or compression, Python lmdb, C liblmdb, or C# can retrieve the original file directly via mdb_get(key).

Reading from Python

import lmdb
env = lmdb.open("wafer.lmdb", subdir=False, readonly=True, lock=False)
with env.begin() as txn:
    bmp_bytes = txn.get(b"Roi_0/Defect_000123.bmp")
    # Save as a BMP file and the original image is restored verbatim

Build

Required tools are Qt 6 (Core, Widgets, and Test for testing), CMake 3.21+, a C++17 compiler, and Git. The LMDB 0.9.33 source is fetched by CMake from the official repository.

PowerShell/MSVC example:

$env:QT_ROOT = 'F:\Qt\6.11.0\msvc2022_64'
cmake --preset qt-msvc-release
cmake --build --preset release
ctest --preset release

If your Qt is installed elsewhere, just change QT_ROOT. Run this from a Visual Studio Developer PowerShell.

Usage

On Windows, we recommend installing LMDBArchiver-<version>-x64.msi from GitHub Releases. The MSI installs the program into Program Files and automatically registers the system-wide .lmdb file association and Explorer context menus. On Windows 11 the menus may appear under Show more options.

1. Use File → New archive to create a .lmdb file.
2. Add entries with the Add file / Add folder toolbar buttons, drag and drop, or by copying files in Explorer and pressing Ctrl+V.
3. Select multiple entries in the tree to extract or delete them. Re-adding to the same internal path replaces the entry with the latest content.
4. If you use the portable ZIP, run Tools → Windows Explorer integration to install the file association and context menus for the current user. For the MSI install, this happens automatically.

For details, see the user guide and the developer guide.

Command-line automation

LMDBArchiverCLI.exe in the distribution package uses the same core without any dialogs.

LMDBArchiverCLI create photos.lmdb C:\Photos
LMDBArchiverCLI create photos.lmdb C:\Photos --compress      # store gzip-compressed
LMDBArchiverCLI add photos.lmdb C:\More --destination imports
LMDBArchiverCLI list photos.lmdb
LMDBArchiverCLI extract photos.lmdb C:\Restored Photos\2026
LMDBArchiverCLI extract photos.lmdb C:\GzOnly --no-decompress  # leave .gz files as-is
LMDBArchiverCLI remove photos.lmdb imports\obsolete.jpg
LMDBArchiverCLI test photos.lmdb
LMDBArchiverCLI compact photos.lmdb

create will not overwrite an existing archive. Omitting the internal path in extract extracts everything.

Packaging

Recommended MSI install package:

scripts\build-msi.ps1 -BuildDirectory build\release -QtBin F:\Qt\6.11.0\msvc2022_64\bin

The script prepares a pinned WiX Toolset 5 in the local build directory, stages the portable distribution files, then produces and validates out/LMDBArchiver-<version>-x64.msi. The generated MSI is not code-signed yet, so we recommend signing it with a Windows code-signing certificate before external distribution.

Portable ZIP:

scripts\package.ps1 -BuildDirectory build\release -QtBin F:\Qt\6.11.0\msvc2022_64\bin

The script uses windeployqt to collect the required Qt DLLs and plugins, the portable MSVC runtime, and the third-party notices, then produces out/LMDBArchiver-<version>-win64.zip.

Current integration scope

A virtual folder implementation identical to Windows' Compressed Folders requires a COM namespace extension with separate installation and signing. The current version delivers what can be distributed reliably: file association, Explorer context menus, drag and drop, and clipboard copy. A future namespace extension can reuse the core library.

License

MIT. The bundled LMDB is distributed under the OpenLDAP Public License.