Cosmos DB vs DynamoDB

Cosmos DB and DynamoDB are the premier fully managed NoSQL databases from Azure and AWS respectively. Both provide global distribution and single-digit millisecond latency, but differ significantly in data model flexibility and consistency options.

Architecture Differences

Cosmos DB is a multi-model database offering five API surfaces: Core (SQL), MongoDB, Cassandra, Gremlin (graph), and Table. Under the hood, it uses the atom-record-sequence (ARS) data model. Data is automatically partitioned and replicated across Azure regions.

DynamoDB is a key-value and document database with a focused data model. Items are organized into tables with partition keys and optional sort keys. Global Secondary Indexes provide alternate access patterns. Global Tables enable multi-region replication.

Performance Characteristics

Both provide SLA-backed single-digit millisecond latency. Cosmos DB backs its latency guarantee with a financially-backed SLA at the 99th percentile. DynamoDB guarantees single-digit millisecond performance with predictable throughput at any scale.

Cosmos DB's unique advantage is its five consistency levels: from Strong (linearizable) to Eventual, with Session, Bounded Staleness, and Consistent Prefix in between. This granularity lets you tune consistency per request, trading latency for consistency exactly as needed.

Trade-offs

Cosmos DB's multi-model capability adds complexity. The RU (Request Unit) pricing model can be hard to predict: different query types consume different RU amounts. DynamoDB's Read/Write Capacity Unit model is simpler, though on-demand pricing simplifies this further.

DynamoDB's AWS ecosystem integration is deeper: Lambda triggers on DynamoDB Streams, Kinesis Data Streams integration, and AppSync for GraphQL. Cosmos DB integrates well with Azure Functions and Azure services but the ecosystem is smaller.

Global Distribution

Both support multi-region writes. Cosmos DB offers automatic conflict resolution policies (last-write-wins, custom). DynamoDB Global Tables use last-writer-wins with eventual consistency across regions.

Real-World Usage

Cosmos DB powers Coca-Cola, Samsung, and the United Nations. DynamoDB runs Amazon.com, Lyft, and Snap. The choice usually follows cloud platform allegiance.

Learn about NoSQL design patterns and global distribution. See our system design guide and pricing.