[kmike]

Originally Posted by JohnWoo

If you have large forum with many different users and user groups and with many forums invisible for some of that usergroups or users, that LEFT JOIN make fulltext search run faster (and sometimes much faster) because some (or many) posts will be excluded from MATCH => AGAINST (and that part of request takes the most part or server load)

Not so.
Typical limiting condition consists of something like:
thread.forumid [NOT] IN(25,197,68,159,193,191,120)
sometimes with posts.userid IN (100,200,300) added.

Now, if you run "EXPLAIN" on resulting queries, you'll see that first index used by mysql is FULLTEXT index on pagetext, and only then threadid index is applied using "where". It means ALL posts are being scanned first using FULLTEXT. The only search type where that LEFT JOIN really limits number of posts to search is a search within thread - EXPLAIN shows that first used index is threadid, and only then fulltext index on pagetext is used.
But... I suspect mysql has a bug here, though - actual search time is exactly the same as without "AND thread.threadid=nnn" condition in WHERE clause, which suggests that fulltext index is used here first anyway.

Second reson is limiting mumber or results returned by search. vb2 version of fulltext search first do lookup in ALL posts with limiting number of matches and after it cut (from that already limited number) more posts looking at user permissions. So, I don't think that vb2 fulltext search works as it must work - sorry

Fulltext hack for VB2 always used boolean mode search, so number of results was much much lower.
Also, now that vb3 has a logic for caching search results, querying all posts and limiting results afterwards depending on user's permission or search preferences suddenly appears quite logical, isn't it? Chances are that another user will run search with the same query, in that case we'll just pick up saved post ids and apply query logic filter to them.