Hi…as per my knowledge after the Mongod process boots up, in addition to being the same as an ordinary process, it loads each binary and reliant library the memory, which serve as the DBMS. It must also be responsible for a large number of tasks such as client connection management, request processing, database metadata and storage engine. All of these tasks involve allocation and freeing up memory, and under default conditions the MongoDB uses Google tcmalloc as a memory allocator. The largest shares of the memory are occupied by “storage engine” and “customer terminal connection and request processing”.