I have a working instance of GeoNode 2.0 over Debian7 (with PostgreSQL) and I want to know where does pyCSW stores the metadata by default. And if it's possible, how to set it to the same PSQL server.
GeoNode comes with pycsw as the built-in CSW instance, so on any GeoNode instance you can connect to the CSW endpoint via
pycsw's GeoNode support works off the same underlying database as GeoNode itself via mappings, so there is no duplication. pycsw uses GeoNode Django/etc. models directly, and GeoNode's defined model mappings to enable seamless/direct access.
Having said this, if you would like to connect pycsw to a GeoNode metadata repository, try the following in the pycsw configuration
database=postgresql://username:password@localhost/database_name # i.e. actual connection to the GeoNode DB
mappings=path/to/mappings.py # identical to https://github.com/GeoNode/geonode/blob/master/geonode/catalogue/backends/pycsw_local_mappings.py
table=base_resourcebase # the internal tablename created by Django