ScyllaDB

ScyllaDB is a wire-compatible, drop-in-compatible rewrite of Apache Cassandra in C++ on the Seastar shared-nothing async framework. Founded in 2015 by KVM and OSv veterans, ScyllaDB delivers the same data model and CQL protocol as Cassandra but with dramatically higher per-node throughput and lower p99 latency — commonly 5–10× faster on equivalent hardware.

Key Features:

• Shard-Per-Core Architecture. Each CPU core owns its own data shard, request queue, and TCP connection. No locks, no shared mutable state — Seastar pins threads to cores.
• Cassandra-Compatible. CQL protocol, drivers, sstable format, gossip, repair tooling all match Cassandra. Existing apps switch by changing the connection string.
• DynamoDB-Compatible API. Optional Alternator interface speaks DynamoDB’s wire protocol — lift-and-shift from DynamoDB without rewriting the client.
• Userspace I/O Scheduler. Cooperative scheduling of disk reads, repairs, compaction, and queries — predictable p99 even under heavy mixed workloads.
• Workload Prioritization. SLA tiers ensure compaction and repair never starve user-facing reads.
• Single-Node Density. Routinely runs 100 TB+ per node; orders of magnitude beyond typical Cassandra footprints.

ScyllaDB vs. Cassandra:

• Throughput. ScyllaDB — ~1M ops/sec per node common. Cassandra — ~100–200K typical.
• p99 latency. ScyllaDB — sub-millisecond; Cassandra — tens of milliseconds during compaction.
• Operational complexity. Similar — same data model, same query language, same multi-DC story.
• Cluster size. ScyllaDB’s per-node density often lets a 5-node Scylla cluster replace a 30-node Cassandra cluster.

Use Cases:

• High-throughput Cassandra workloads where node count or cost has become a problem.
• Real-time ad-tech, gaming leaderboards, IoT telemetry — tail-latency-sensitive workloads.
• DynamoDB migrations seeking open-source alternative without rewriting the client (Alternator API).
• Multi-region deployments where Cassandra’s p99 jitter under repair is unacceptable.