PostgreSQL is a well-designed, open-source multi-purpose relational database system which is widely used throughout the world.

It is one huge system with the integrated subsystems, each of which has a particular complex feature and works cooperatively with each other. Although understanding of the internal mechanism is crucial for both administration and integration using PostgreSQL, its hugeness and complexity make it difficult.

The main purposes of this document are to explain how each subsystem works, and to provide the whole picture of PostgreSQL.

This document covers versions 17 and earlier.

Some academic papers have referred to this document. The Chinese version of this document was published in June 2019.