tl;dr:A significant overhaul of the Query Execution Engine has been announced. The article provides an in-depth look into the technical aspects of this change. The previous engine, termed "Classic," was built around JSON documents, leading to inefficiencies in complex queries. The new Slot Based Engine (SBE) introduces "slots" as a means to pass data, optimizing the process. Nikita delves into the architecture, data flow, and challenges faced during the transition.