With the release of SQL Server 2012, Microsoft introduced a new type of nonclustered index called xVelocity columnstore index in the SQL Server database engine. It is based on VertiPaq in-memory data compression technology. The xVelocity memory optimized columnstore indexes are one of the most significant performance and scalability enhancements in SQL Server 2012. The xVelocity columnstore indexes speed up the processing time for common data warehousing queries — particularly in situations where very large quantities of data have to be aggregated and accessed quickly. According to Microsoft, under certain conditions, the xVelocity columnstore index provides queries with speed improvements of 4X, 10X or even 100X.
Checkout my article here, in which I discussed how these indexes work and how the data is stored in a columnstore index.
This article is published on SearchSQLServer.techtarget.com.