MongoDB is an open source document-oriented NoSQL database system that is used for high-performance, high-availability and easy scalability. This document aims to provide a comprehensive guide for exploring the source code of the MongoDB project.

The first step in exploring the source code of MongoDB is to download and set up the project. First, obtain the source code from the MongoDB official website or from the associated GitHub mirror. The source should be compiled into a binary for the intended platform and, if necessary, an install script should be used to install and configure MongoDB.

Next, it is important to be familiar with the source code organization of MongoDB. The source code is organized into libraries and command-line tools that communicate with the MongoDB server. The server is composed of the following components: the storage engine, query language, replication manager, and storage recovery system.

The storage engine is the core of MongoDB. It is responsible for storing and managing documents. It includes the WiredTiger storage engine, which supports document-level locking and indexing capabilities. The query language is responsible for parsing and executing queries. It also handles query optimization and execution plan generation. The replication manager is responsible for ensuring the reliability and performance of MongoDB cluster. And the storage recovery system is responsible for ensuring data durability in case of unexpected system shutdowns.

Once a basic understanding of the overall architecture of MongoDB is gained, it is a good idea to explore the source code in depth. One way to do this is to start designing and implementing a feature from scratch. If a feature is already implemented, “dissecting” it can be done for a better understanding. Looking at the relevant source code and analyzing it can also be helpful in understanding how the code works and what decisions were taken during its development.

Finally, it would be beneficial to read documentation related to MongoDB. Official MongoDB documents and blogs can help gain a better understanding of the source code. Additionally, relevant books can also provide an in-depth look into the implementation of the source code.

In conclusion, this document provides a comprehensive guide for exploring the source code of the MongoDB project. It outlines the process of downloading, setting up, and understanding the architecture of the MongoDB codebase. It also provides tips and guidance on further investigation into the source by reading official documentation and books. With this guide, developers can gain a deeper understanding of the internals of MongoDB and the open source community.