Joedb, the Journal-Only Embedded Database

Joedb is a light-weight C++ database that keeps tabular data in memory, and writes a journal to a file. The whole data history is stored, so it is possible to re-create any past state of the database. Joedb has a network protocol, and can operate in a distributed fashion, a bit like git for data. It provides ACID transactions for local and remote concurrent access to a file.

The diagram below illustrates how the system works: joedbc, the joedb compiler, reads the database schema and produces classes that can be used to manipulate files:

Other systems such as protocol buffers provide similar type-safe mechanisms for serializing structured data, but are missing key properties of a database, such as concurrency, transactions, and incremental crash-safe updates. Joedb can offer all these features by storing data as a journal of transactions.

To give an indication of joedb's simplicity, the table below shows the size of joedb's source code compared to some other libraries. Lines of code are counted with wc -l. Compressed size is the size in bytes after removing comments and compressing with gzip. These numbers were measured on 2024-07-28 on the main branch.

Software	Lines of code	Compressed size	Notes
joedb	19,288	72,268	without tests
nlhohmann/json	24,941	87,168	single include
boost/json	37,609	123,229
SQLite	258,281	1,067,983	sqlite3.c amalgamation
PostgreSQL	1,513,329	5,250,316	content of src dir, without tests

So joedb is an extremely simple low-level foundation for sharing relational data. It would be possible to build a SQL database on top of it, but it is already very convenient by itself.

For more information, please take at a look at the documentation.