How is the source code organized?
If you point your browser at How PostgreSQL Processes a Query, (also in a checkout of the source code, under src/tools/backend/index.html), you will see few paragraphs describing the data flow, the backend components in a flow chart, and a description of the shared memory area. You can click on any flowchart box to see a description. If you then click on the directory name, you will be taken to the source directory, to browse the actual source code behind it. We also have several README files in some source directories to describe the function of the module. The browser will display these when you enter the directory also. Other than documentation in the source tree itself, you can find some papers/presentations discussing the code at http://www.postgresql.org/developer/coding. An excellent presentation is at http://neilconway.
