Pebble and FoundationDB are apples and oranges. Pebble is per-node KV storage engine. FoundationDB is a distributed multi-modal database. Internally, FoundationDB uses a library like Pebble for the per-node data storage. I think at one point it used SQLite. I'm not up to date on what it currently use. I seem to recall FoundationDB was writing their own btree-based node-level storage engine to replace the usage of SQLite.

The equivalent of FoundationDB is present inside of CockroachDB: a distributed, replicated, transactional, KV layer. This is where a big chunk of CockroachDB value resides. This is where our use of Raft resides. Pebble lies underneath this.

The current production storage engine is an old-ish version of the SQLite btree. A new btree engine is being written now and is available but I don’t know if it is being used in production anywhere.

RocksDB is shipping soon thanks to some work by members of the community.