1. Setting up PostgreSQL in Eclipse
  2. Steps in building and running PostgreSQL
  3. A tour of PostgreSQL by Tom Lane
  4. Internals of PostgreSQL for database administrators and System Developers by Hironobu Suzuki
  5. How to use the debugger to explore PostgreSQL
  6. Intro to Hacking PostgreSQL by Gavin Sherry (Read sections upto and including Conventions; you can skip sections on submitting a patch and real code for now.)
  7. Hacking PostgreSQL by Neil Conway (Read sections upto and including Architecture, skip sections from common code conventions onwards for now).
  8. PostgreSQL internals through pictures by Bruce Momjian
  9. An Introduction to Hacking PostgreSQL by Neil Conway and Gavin Sherry
  10. PostgreSQL (current version) internals documentation at postgresql.org (gives quite a bit of information)
  11. Bruce Momjian's presentations on PostgreSQL internals
  12. Other Useful PostgreSQL links