Cassandra vs ScyllaDB vs DynamoDB: Wide-Column Stores Compared

If you need wide-column at scale, you have three viable options. The right pick depends on your operational stomach.

Cassandra: the OG

Cassandra is the original wide-column store: open-source, mature, tunable consistency. The trade is operational complexity; runs well only with Cassandra-experienced engineers and the headcount budget for the ops tier.

• Open-source plus mature. Decade-plus of production use; the patterns and pitfalls are well documented; community is active.
• Tunable consistency. Per-query consistency level (ONE, QUORUM, ALL); the operator picks the consistency-vs-latency tradeoff per call.
• Operational tax. Repairs, compactions, gossip; Cassandra does not run itself; needs hands-on operation.
• Sweet spot. Teams with Cassandra muscle and budget for 2-3 dedicated DBAs at scale; the ops tier is the cost.

ScyllaDB: same data model, faster

ScyllaDB is the C++ rewrite of Cassandra. Same data model, same CQL API, significantly faster and lower-resource. The right call when you outgrew Cassandra performance but want to keep the data model.

• C++ rewrite. Shard-per-core architecture; bypasses JVM overhead; throughput per node is multiples of Cassandra.
• Same Cassandra API. CQL-compatible; existing Cassandra clients work; migration is mostly mechanical.
• Lower resource use. Fewer nodes for the same workload; the cluster shrinks; the bill drops.
• Sweet spot. Outgrew Cassandra performance; team wants to keep the data model; willing to operate the database themselves.

DynamoDB: managed-only path

DynamoDB is AWS-managed wide-column. No cluster to operate, no patches to apply, no failover to engineer; the trade is AWS lock-in and per-request cost. The right call for AWS-committed teams that want to skip the ops entirely.

• AWS-managed. No cluster, no patches, no failover engineering; the operational story is "submit and pay."
• Provisioned or on-demand. Provisioned for predictable workloads; on-demand for spiky; pick based on traffic shape.
• Auto-scales. Capacity adjusts automatically; the operational concern shifts from cluster size to key design.
• Sweet spot. AWS-committed; want zero database ops headcount; willing to pay the per-request premium.

Cost and ops compared

At 100K writes/sec the monthly cost spread is roughly 5x. Cassandra and ScyllaDB win on unit cost; DynamoDB wins on ops headcount; the right pick depends on which line item is bigger for you.

• Cassandra self-managed. ~$5k/mo for the infrastructure; add 2-3 DBAs at headcount cost; total cost dominated by people.
• ScyllaDB self-managed. ~$3k/mo for the infrastructure; same DBA cost; lower unit cost is the savings.
• DynamoDB on-demand. ~$15k/mo at this volume; provisioned ~$8k/mo with reserved capacity; zero DBA cost.
• The honest math. Below $50k/mo cloud bill, DynamoDB wins on total cost; above, self-managed wins as DBA cost amortises.

Antipatterns

• Cassandra without operational maturity. Outage time exceeds savings.
• DynamoDB with poor key design. Hot partitions; cost explodes.
• Migrating between them every 18 months. Data has gravity.

What to do this week

Three moves. (1) Run a 30-day trial of the candidate against your real workload. (2) Compare TCO + workflow fit, not just feature checklists. (3) Decide and commit; running both in parallel is the most expensive option.