Jeffro notes:It was also mentioned that most of the [intensive search] functionality can be achieved using Google Custom Search. In fact, Matt Mullenwegs personal WordPress site Ma.tt runs Google Custom Search. I wonder if that reflects that Matt prefers the Google service; that he is steering regular WordPress users to a practical solution, or is sparing the environment/farm on which his domain resides.

Caching and pre-indexing are helpful. At one time, it was rather common for document-search facilities to pre-index. Once the simple term-indexing is done, then more elaborate search-strategies can work off the indexes.

WordPress caching plugins routinely cache search-results. An appropriately regulated background indexer could make the cache into a more-overt/robust search-enhancement.

Fancy searches do require additional levels of involvement ... and of course, for many folks & enterprises, the off-site cloud-based search-service [see: Review – Swiftype Search Plugin] is just the ticket.

For some folks & situations, though, there can be attractions & values in taking a more hands-on approach with search-functionalities. It becomes a database & data-processing undertaking: indexes of terms found within the site form the data, and query-facilities process it and return hits (taking input from the advance search interface).

A search of WordPress Extend using 'sqlite + cache' returns 4 plugin titles, 2 that look interesting.