verneuil VS WCDB

It'd be process wide. If you want an example can check out the example using a vfs here. There's an explicit passing of vfs there and an implicit usage of it. https://github.com/backtrace-labs/verneuil/blob/main/examples/rusqlite_integration.rs

It doesn't even have to be WAL-based system. Backtrace Labs has a SQLite virtual file system (VFS) called Verneuil that works similarly but works with the rollback journal instead of the WAL.

https://github.com/backtrace-labs/verneuil/ is one way to address the diffing / read replica part of the problem. I believe it's compatible with gossipping: most of the data is in small content-addressed chunks, with small manifests that tell clients what chunks to fetch and how to reassemble them to recreate a sqlite database. There's already client-side caching to persistent storage, and chunks can be fetched on demand.

Sharing replication data P2P, while retaining the simplicity of a single authoritative writer per database, is explicitly part of the project's long-term goals!

WCDB - WCDB is a cross-platform database framework developed by WeChat. Language: C.

SQLite is so ubiquitous you'd be hard pressed to find an app or service that doesn't use it.

Look through the licenses for the software included as part of your phone's OS. You'll find SQLite in there.

Search GitHub for sqlite, there are several projects with thousands of stars that use SQLite. Here's one: https://github.com/Tencent/wcdb