This plugin port the full text index search functionality from mediawiki (ver 1.19.0) to wordpress.
Currently this plugin will not change the original wordpress search function. If you like to use it there are some custom function you need to add to your theme.
hook the "save_post" action to choose which post you need to store full text to this plugin.
// $fulltext can be $_POST['post_title'] or $_POST['content'] ... etc or combine each together
hook the "posts_clauses_request" filter to add additional JOIN and WHERE with the search keywords to the exist SQL pattern.
$key = get_query_var('key');
Remember to remove filter in the "posts_clauses_request" filter function because you just need to run it once.
The original WP_Query use SQL_CALC_FOUND_ROWS to calculate the total, if you have lots of post, you can add "no_found_rows" to WP_Query's arguments and do the count yourself by adding second parameter to hook "posts_clauses_request".
The example of the "posts_clauses_request" filter: https://gist.github.com/2761739