google/leveldb

LevelDB is a fast, embedded key-value storage library created at Google. Think of it as a very efficient dictionary built into your application: you give it a string key and a string value, and it stores them for you in a way that keeps everything sorted and retrievable extremely quickly. The basic operations are simple, store a value, retrieve a value, or delete a value, but those three primitives can underpin a wide range of applications that need to persist structured data without the complexity of a full database. LevelDB achieves its speed through a design called a Log-Structured Merge-tree, or LSM-tree. Rather than writing directly to a fixed location on disk for every change, it batches writes into memory first, then flushes them to disk in sorted segments called SSTables. When you read data, it merges those segments intelligently to find the latest version of a key. Data is automatically compressed using the Snappy algorithm (with Zstd as an option) to save disk space. It also supports atomic batch writes and consistent snapshots, meaning you can read a stable view of the data even while writes are happening. You would use LevelDB when you are building an application in C++ (or via bindings in other languages) that needs fast, reliable local storage without running a separate database server. It is not a SQL database and does not support network clients, only one process can open a database at a time. It is a good fit for embedded use cases like browser storage engines, mobile apps, or backend systems that need a lightweight, high-performance local store. The repository is written in C++ and built with CMake.