CockroachDB vs NuoDB: What are the differences?

Introduction CockroachDB and NuoDB are both distributed SQL databases that are designed for scalability and high availability. Although they share some similarities, there are key differences between the two.

1. Storage and Replication: CockroachDB uses multi-version concurrency control (MVCC) to manage storage and replication. It stores data in key-value format and replicates it across multiple nodes in a cluster. NuoDB, on the other hand, uses a distributed, in-memory architecture with a peer-to-peer approach for data replication. It divides data into "atoms" and distributes them across multiple nodes.

2. Consistency Model: CockroachDB offers strong consistency guarantees, ensuring that all replicas are always up-to-date and in sync. It uses a distributed consensus algorithm (RocksDB) to achieve consensus on data changes. In contrast, NuoDB provides eventual consistency, allowing replicas to diverge temporarily before reconciling. It uses a quorum-based algorithm (Paxos) to handle conflicts and achieve eventual consistency.

3. SQL Compatibility: CockroachDB is fully compatible with PostgreSQL, supporting its SQL syntax, data types, and even some of its extensions. This makes it easier to migrate existing applications built on PostgreSQL to CockroachDB. In contrast, while NuoDB also supports SQL, it does not offer full compatibility with any specific SQL dialect.

4. Scale-out Architecture: CockroachDB is designed to scale horizontally by adding more nodes to the cluster, allowing for increased performance and storage capacity. It uses automatic sharding and rebalancing to distribute data across nodes and maintain load balance. NuoDB also supports scale-out but takes a different approach by allowing applications to add or remove nodes dynamically without disruption. It offers elastic scaling capabilities without the need for sharding or rebalancing.

5. Data Distribution: CockroachDB automatically distributes data across nodes by splitting it into ranges based on primary key values. This ensures that data is evenly spread and can be accessed in parallel from different nodes. NuoDB, on the other hand, distributes data using its "atoms" technique, which allows for greater flexibility in data placement and reduces data movement during scaling or rebalancing.

6. ACID Compliance: CockroachDB ensures ACID (Atomicity, Consistency, Isolation, Durability) properties for transactions, guaranteeing data integrity and reliability. It supports distributed transactions and provides serializable isolation level. NuoDB also offers ACID compliance but has a different approach to transaction management, using a distributed, peer-to-peer architecture instead of a centralized transaction coordinator.

In summary, CockroachDB and NuoDB differ in their storage and replication strategies, consistency models, SQL compatibility, scale-out architectures, data distribution techniques, and transaction management approaches.