"Main search engine" would be the search feature, but not browsing/category listing?
That's correct, just the search function, though I'm looking into using Solr for other types of browsing.
Are you using Solr for all data storage and search? Or a RDBMS? If so, what is the split?
All data is in an RDBMS (MySQL) and there's an update process to keep Solr synchronized with it. Kevin
