CockroachDB vs MemSQL: What are the differences?

## Introduction
Key differences between CockroachDB and MemSQL.

1. **Architecture**: CockroachDB is a distributed SQL database that uses a distributed, transactional key-value store as its underlying engine. In contrast, MemSQL is a distributed, in-memory, SQL database that uses a combination of in-memory rowstore and on-disk columnstore for its storage.

2. **Consistency Model**: CockroachDB offers strong consistency guarantees based on the linearizable consistency model, ensuring that all reads and writes are globally ordered. MemSQL, on the other hand, provides eventual consistency by default but can be configured for strong consistency using its distributed lock manager.

3. **Scale-out Capabilities**: CockroachDB is designed for horizontal scalability, allowing users to easily add nodes to the cluster to handle increased workloads. MemSQL also supports scale-out capabilities, but its in-memory design may limit the scalability compared to CockroachDB for certain workloads.

4. **SQL Support**: Both CockroachDB and MemSQL support ANSI SQL, providing familiar query language interfaces for users. However, MemSQL also offers support for MySQL wire protocol, making it compatible with existing MySQL applications without significant modifications.

5. **Storage Options**: CockroachDB uses a distributed, multi-version concurrency control (MVCC) approach for data storage, ensuring data consistency and isolation. In contrast, MemSQL leverages a combination of in-memory and on-disk storage engines, providing high-performance queries for analytical workloads.

6. **Community and Licensing**: CockroachDB is an open-source project under the Apache License 2.0, allowing users to contribute and modify the code freely. MemSQL, on the other hand, offers both a free community edition and a paid enterprise edition with additional features and support options.

## Summary
In Summary, CockroachDB and MemSQL differ in their architecture, consistency model, scale-out capabilities, SQL support, storage options, and community/license offerings.