# MMKV — Efficient Mobile Key-Value Storage Framework by WeChat

> MMKV is a high-performance key-value storage framework developed by WeChat. It uses memory-mapped files and protobuf encoding to deliver fast, reliable persistence on Android, iOS, macOS, Windows, and POSIX systems.

## Install

Save as a script file and run:

# MMKV — Efficient Mobile Key-Value Storage Framework by WeChat

## Quick Use
```bash
# iOS (CocoaPods)
pod install MMKV

# Android (Gradle)
implementation 'com.tencent:mmkv:2.0.1'

# Python
pip install mmkv
```

## Introduction
MMKV is an efficient, small, and easy-to-use mobile key-value storage framework created by the WeChat team at Tencent. It relies on memory-mapped files (mmap) for persistence and Protocol Buffers for serialization, achieving read and write speeds that far exceed SharedPreferences and NSUserDefaults.

## What MMKV Does
- Provides persistent key-value storage using memory-mapped files for near-instant writes
- Supports multiple data types including strings, integers, floats, byte arrays, and custom Parcelable/NSCoding objects
- Offers multi-process concurrent read/write on Android via file locking
- Delivers cross-platform support for Android, iOS, macOS, Windows, POSIX, and HarmonyOS
- Enables data encryption with AES-128/CFB for sensitive values

## Architecture Overview
MMKV maps a file into virtual memory using mmap, so writes go directly to the kernel page cache without explicit I/O calls. Data is encoded with Protocol Buffers in an append-only log. When the file grows beyond a threshold, MMKV performs a full rewrite to reclaim space. A CRC checksum guards against corruption from unexpected process termination.

## Self-Hosting & Configuration
- Add the dependency for your platform (CocoaPods, Gradle, pip, or CMake)
- Initialize MMKV once at app startup with a root directory path
- Optionally set a per-instance encryption key for AES-128 protection
- Enable multi-process mode on Android by passing MMKV.MULTI_PROCESS_MODE
- Tune the page-size or file-growth strategy for workloads with very large values

## Key Features
- Blazing speed: benchmarks show 1000x faster than SharedPreferences on Android
- Tiny binary size of roughly 400 KB on mobile platforms
- Thread-safe and multi-process-safe with granular file locks
- Automatic data migration helpers from SharedPreferences and NSUserDefaults
- Mature and battle-tested in WeChat, serving over a billion monthly active users

## Comparison with Similar Tools
- **SharedPreferences** — Android-only, synchronous XML I/O, much slower for frequent writes
- **NSUserDefaults** — Apple-only, plist-backed, no encryption or multi-process safety
- **DataStore (Jetpack)** — Google's modern replacement for SharedPreferences, but Android-only and coroutine-based
- **Realm** — Full object database with queries, heavier footprint than a simple KV store
- **LMDB** — Also mmap-based, but targets server workloads and lacks mobile-first APIs

## FAQ
**Q: Does MMKV handle process crashes safely?**
A: Yes. Because mmap writes go to the OS page cache, data survives app crashes. A CRC check detects partial writes on next load.

**Q: Can I use MMKV as a general-purpose database?**
A: MMKV is designed for flat key-value data. For relational or document data, use a proper database like SQLite.

**Q: How large can an MMKV file grow?**
A: There is no hard limit, but MMKV is optimized for many small values. Files over tens of MB may trigger more frequent full-rewrites.

**Q: Is MMKV open source?**
A: Yes. MMKV is released under the BSD 3-Clause license on GitHub.

## Sources
- https://github.com/Tencent/MMKV
- https://github.com/Tencent/MMKV/wiki

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Source: https://tokrepo.com/en/workflows/asset-4f654acd
Author: Script Depot