Okcupid.com (can find matches without accessing a database!?) I'm doing a research project on a popular dating site called: OkCupid
I would like to talk about how the database is used.
After reading this explanation from the Co-Founder of the site, I became very confused.
The statements:  


  when a user performs a match search on OkCupid, we have to do the
  following:
  
  -Retrieve (from somewhere not the DB) their question answers, their ideal match's answers, and their question importances. On average,
  each user on OkCupid has 250 questions answered in 3 parts.
  -Figure out who qualifies for their search, typically a very complicated query across a few million users. On average, tens of
  thousands of people qualify, and we need to figure out who they are
  without hitting the DB.  


How do they do all this without consulting a database??
I'm utterly confused.
Here is a link to the post
I appreciate any explanations as to how they do things there
They didn't explicitly mention this, so I am only guessing here, but they are using some search index such as Lucene to perform the actual searches.  They'll have a persistent database of some sort but their search index is periodically built from that data set.