YugaByte only added distributed transactions in the new 1.1 release (previously, it only supported single-row transactions). The architecture is a variation on 2PC and seems sound, but I think it's fair to say that it's early days. Meanwhile, Cockroach and TiDB both have battle-tested implementations.

YugaByte is pretty quirky. Rather than settle on a native data model, they offer several "personalities" that mimic other products (Cassandra, Redis and PostgreSQL), and you can mix and match them. But they've implemented each API with their own set of weird warts. For example, their CQL implementation has CREATE INDEX, but it does not index existing data [1]. You have to either create the secondary index before inserting data, or force a reindex of everything with a dummy UPDATE statement. Who would ship such a product?

More warts/Cassandraisms: UPDATE is actually an upsert; an update that doesn't match a row will insert it. And SELECT ... WHERE expressions can only use AND expressions (!) [2].

Hopefully the forthcoming SQL API should be saner, but it's very limited at the moment. It does not seem to support joins, transactions or indexes, for example. Meanwhile, CockroachDB and TiDB both have rich SQL implementations, including joins and aggregations, with cost-based query optimizers that can take advantage of multiple indexes and table statistics.

It seems more appropriate to compare YugaByte with distributed key/value stores like FoundationDB, Cassandra, Scylla and Redis.

[1] https://docs.yugabyte.com/latest/explore/transactional/secon...

[2] https://docs.yugabyte.com/v1.0/api/cassandra/dml_select/#roo...