[wwilson]

Full disclosure: I now work at Google on Cloud Spanner which competes with both products you mentioned. These are just my personal (and probably highly biased) opinions.

I have some concerns about CockroachDB on both the performance and the reliability fronts. But I hugely admire what they're trying to do and I've heard that they're rapidly improving in both areas. TiDB is an exciting project that I've heard great things about but have never tried myself. I think it's also relatively immature.

Honestly if I were starting a project right now and had neither FDB nor Spanner available to me, I'd probably try to push Postgres as far as I possibly could before considering anything else.

[lobster_johnson]

Agreed, Postgres does scale very well for non-Google-sized apps, though a lingering issue is handling failover.

But if one does need a bit more horizontal scalability, there don't seem to be a lot of options if you also want atomic, transactional updates (though not necessarily strict transaction isolation). I have an app that is conceptually a versioned document store, where each document is the sum of all its "patches"; when you submit a batch of patches, the rule is that these are applied atomically, and that the latest version of document thereafter reflects your patch (optimistic locking and retries take care of serialization and concurrent conflicts). I'm using PostgreSQL right now, which does this beautifully, but with limited scalability. I've looked for a better option, but not come up with anything.

Redis would handle this, but it would work purely thanks to single-threaded; and I don't feel like Redis is safe as a primary data store for anything except caches and such. Cassandra might do it, using atomic batches, although its lack of isolation could be awkward to work around.

[macdice]

What do you think Postgres should do in this area? It seems there are a bunch of approaches being explored by different teams. I'd be very interest to hear a Spanner person's take.