Scylla is a new open source NoSQL database that is compatible with Apache Cassandra but provides significantly higher performance through a redesign that takes advantage of modern hardware. Scylla is capable of over 1.8 million operations per second per node with predictable low latencies. It uses an architecture with shard-per-core and reactor programming that avoids locks and threads for near-linear scaling. Scylla also has its own efficient unified cache and I/O scheduler that maximize throughput and allow it to outperform Cassandra on benchmarks by an order of magnitude. Scylla is fully compatible with Cassandra and aims to build an open source community around ongoing core database improvements.