Production crawls are indexed for full text search 7 days after they finish. To do this we use a special bundling of the Nutch search engine called NutchWAX (Nutch + web archiving extensions). Nutch indexes every word on every archived page. Results are determined in two ways: Nutch compares the number of times that your search term appears on a document with the number of times that the term appears in the overall corpus of archived pages; secondly, Nutch keeps track of how many pages refer to a document and what the anchor text is for those referrals.
To learn more about NutchWAX, visit its homepage at: http://archive-access.sourceforge.net/projects/nutchwax/