In-Memory OLTP is the name of the optimistic concurrency model implementation offered from SQL Server 2014 onwards. The challenge that In-Memory OLTP is designed to solve is the ability to process massively concurrent transaction workloads, while removing the logical limitations of the pessimistic concurrency model present in the traditional transaction processing engine in SQL Server. Microsoft also wanted to introduce In-Memory OLTP as an additional transaction processing engine and not as a replacement for the standard transaction processing engine. This decision was made to ensure that existing applications running on SQL Server would be compatible with newer SQL Server versions, but offer the ability to allow newer applications to take advantage of the new engine without separating the two systems.
In this section, we will take a look at the architecture of the In-Memory OLTP engine and see how data is stored and processed.