- No GC Tuning. It just works out of the box and I don't sleep over requests being dropped because of a multi-second GC.
- Compactions are fast. Compactions in Cassandra generate a lot of garbage (which cause a lot of GC), and end up taking a long time. This becomes worrisome as your largest, most compacted tables tend to be the ones you write a lot too - so performance degrades over time (until you have to shard again).
Cassandra is still very good software though and still a solid choice - it was far more stable than Mongo (pre-WiredTiger, I haven't used mongo past ~2.2), and while the above issues were annoying, they were entirely predictable. Capacity planning was easy, and with Scylla you may find yourself running fewer nodes (maybe DSE prefers Java because they charge per core, jk).
The only thing I've missed in Scylla so far is LWTs, but I have not used that much.
EDIT: looks like LWTs are still unavailable https://github.com/scylladb/scylla/issues/1359
We're using it now as we approach Alpha, and love it. Extra bonus - no Zookeeper!
* Scylla 3.0, which adds secondary indexes and materialized views; and
* OLTP and OLAP features, which are not ready.
I'm struggling to find any clear information on what's implied by OLTP, but from the roadmap [1], it looks like they're just adding Cassandra's LWTs, not ACID transactions. Last I heard, you couldn't build ACID on top of Cassandra/Scylla, since row updates across multiple keys cannot be done atomically. Calling this OLTP seems a little misleading.
[1] https://www.scylladb.com/product/technology/scylla-roadmap/
And I don't think OLTP/OLAP is about LWTs. I think they are just talking about Scylla's ability to process normal updates in a timely manner while doing OLAP queries.
And you're right about ACID transactions. Multiple rows across two or more partitions can not be updated atomically, even with LWTs, but it is possible for a single partition.
Cassandra is even starting to use some of the architectural ideas from Scylla but it's stuck in a messy state so far. Scylla has the opportunity to cleanup and make forward progress with a solid technical foundation.
