Ask HN: P2P Databases?

Git. Seriously, git is, depending on your data model, possibly the best delta compression and sync model you can find. There pitfalls and sync issues to consider, but if it's just going to be published by one authority, git is a great solution.

Couchbase Lite offers delta-sync and P2P replication over any transport. Has client libraries for all mobile OSes, Java, and recently C.

CBL is backed largely by Sqlite with features layered on top. Local query support, server replication and a bunch of other nice features useful for an offline/P2p database.

Disclaimer: Employee working on the server-side Sync Gateway component for Couchbase Mobile.

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!

Ignite works as you describe:

https://ignite.apache.org/

I wouldn't really recommend this approach, I would think more in terms of subscriptions and topics and less of a 'database'.