• include:   *.h files with global definitions (constants, types, ...)
• backend:   code for PostgreSQL database engine
• bin:   code for clients (e.g. psql, pg_ctl, pg_dump, ...)
• pl:   stored procedure language interpreters (e.g. plpgsql)
• interfaces   code for low-level C interfaces (e.g. libpq)

Code for backend (DBMS engine)

• ~2000 files (~1100.c, ~900.h, 8.y, 10.l),   1.5×10⁶ lines of code