Kdb+ vs XAP: What are the differences?

Kdb+: Fast, powerful, massively scalable time-series database. It is a column-based relational time-series database with in-memory abilities. The database is commonly used in high-frequency trading to store, analyze, process, and retrieve large data sets at high speed. kdb+ has the ability to handle billions of records and analyzes data within a database; XAP: The In-Memory computing solution to scale your applications. It provides an essential set of data store features, such as transactions, indexes, and query language (SQL-like queries). It also handles common functions such as messaging, event processing, data access, and transaction processing (ACID compliant) completely and exclusively in-memory.

Kdb+ and XAP belong to "In-Memory Databases" category of the tech stack.