Thanks for putting this together. I wonder, is Postgres a bit of a large DB if it's just a personal website search tool? I'll have to give it a go. We need more tools like this.
Postgres is just used for the site admin, i.e. keeping track of submissions, review status, subscriptions etc. The actual search index is in Apache Solr. In theory you could use Solr to store all the admin data, but it is generally not recommended to use a Solr style document store to master data. I guess something more lightweight like SQLite could be used, but it is intended to be deployed on servers and Postgres isn't too resource intensive.