The best source of the early Google codebase is a talk given by Jeff Dean himself. The talk describes Google1997, Google1999, Google2001, Google2004, Google2007 in some considerable details, from architectural diagrams to low-level bit packing tricks.

http://research.google.com/people/jeff/WSDM09-keynote.pdf

It's an overview of highly-optimized solutions to difficult problems, I am more interested in elegant code (beautiful + maintainable) - this is why I asked. Something makes me skeptical there could be any at such stage, when shipping is most important.