I think Apache Ignite distributed KV store is much better choice as it has 2PC, indexes, distributed computing idioms and can be embedded as library in JVM app.

I think Apache Ignite distributed KV store is much better choice as it has 2PC, indexes, distributed computing idioms and can be embedded as library in JVM app. Plus it supports SQL engine, thanks to H2 SQL parser engine. You can also create graph layer over it using gremlin in a day or two.