I intend to have a Drupal 6 site with some cutom node types indexed by ApacheSolr using the XML Schema provided. However, I'd like to add a lot of gigantic indexes to it that reside only in the Lucene/Solr system (ha) and not physically in my Drupal MySQL database. For example, I may have a thousand or even a hundred thousand nodes in Drupal, but I might have ten different "external" indexes with millions of records each, and I'd like to conduct faceted search against the whole lot of 'em.
How do I go about appending multi-million-record indexes to my working Drupal 6 + ApacheSolr configuration so that I can search across the universe?
I anticipate (ultimately) hundreds of millions of very tiny data in these indexes with a sweatshop of Lucene servers, but only one Drupal site. So of course I can't just create hundreds of millions of nodes in my poor little MySQL server.
I know this is a complex and wide-scoping question so of course I'm hoping for general pointers to appropriate reference material.