I have spent quite some time researching how a database works internally and I thought to write about what I have learned so far. A database system consists of many components like the query planner, the query execution engine, the storage engine, the data replication and sharding mechanisms, etc. The key component is the storage engine, which determines how the data is represented, accessed and stored. It consists of several different components, but at the core of almost all database storage engines there is a data structure, named B-tree, around which all the other modules revolve. Let’s explore why is it so.