1. Data Model: Kdb+ follows a columnar data model, where data is stored in columns rather than rows. This allows for efficient querying and high performance when working with large datasets. On the other hand, MemSQL follows a row-oriented data model, where data is stored in rows. This makes it more suitable for transactional workloads.

2. Concurrency Control: Kdb+ implements a unique form of concurrency control known as snapshot isolation. This ensures that each transaction sees a consistent snapshot of the database at a specific point in time, avoiding conflicts and ensuring data consistency. In contrast, MemSQL uses traditional concurrency control techniques like locking and multi-versioning to handle concurrent transactions.

3. Scalability: MemSQL is designed to scale horizontally, allowing you to add new nodes to a cluster to handle increasing data volumes and query loads. It also supports automatic data sharding, which allows data to be distributed across multiple nodes. On the other hand, while Kdb+ can be horizontally scaled to some extent, it is primarily optimized for single-node performance and may not provide the same level of scalability as MemSQL.

4. SQL Compatibility: MemSQL offers full SQL compatibility, allowing you to use standard SQL queries to interact with the database. This makes it easier for developers and analysts familiar with SQL to work with the system. In contrast, while Kdb+ has some SQL-like functionality, it uses its own query language called q, which has a different syntax and semantics. This may require some additional learning curve for users who are not familiar with q.

5. Data Compression: Kdb+ offers advanced data compression techniques, which can significantly reduce data storage requirements without compromising query performance. This is particularly useful for applications with large data volumes. MemSQL also supports data compression, but it may not provide the same level of efficiency as Kdb+ in terms of compression ratios and query performance.

6. Data Integration: MemSQL provides built-in connectors for a wide range of data sources and supports real-time data ingestion, making it well-suited for streaming and real-time analytics use cases. Kdb+ also supports data integration, but it may require additional development effort to build custom connectors or handle real-time data ingestion.

In Summary, Kdb+ and MemSQL differ in their data models, concurrency control mechanisms, scalability options, SQL compatibility, data compression capabilities, and data integration features. Choosing between them would depend on the specific requirements of your application and the trade-offs that you are willing to make in terms of performance, scalability, and ease of use.