Thinking about two post tables idea, it could go really well along with mysql replication.
Idea: set up second mysql server (even on the same physical machine), set it up to replicate post table from main forums db. All updates to that second mysql server will be handled by only one slave thread, and it could be locked freely without any effect on first mysql server perfomance.
Since JohnWoo's hack uses two tables in the main query, it appears that thread table need to be replicated along with post table.
Changes to current hack code would be really small: initialize another db connection and fire query to a second db instead of main one.

I don't plan to implement this any time soon, though accidentally we have workng replication of our forum db to another server. I'm polishing a vb2-like hack of this (JohnWoo's) hack :) . It eliminates LEFT JOIN and always searches IN BOOLEAN MODE. Had to drop search by relevance though, I highly doubt someone used it even once though.

i will try..and see what happen. Allway can come back .

i dont have to wait to much...

and work Fine whit 3.0.1

mysql> ALTER TABLE post ADD FULLTEXT (title);
Query OK, 1762278 rows affected (4 min 2.67 sec)
Records: 1762278 Duplicates: 0 Warnings: 0

mysql> ALTER TABLE post ADD FULLTEXT (pagetext);
Query OK, 1762278 rows affected (14 min 59.70 sec)
Records: 1762278 Duplicates: 0 Warnings: 0

mysql> OPTIMIZE TABLE post;
+----------+----------+----------+----------+
| Table | Op | Msg_type | Msg_text |
+----------+----------+----------+----------+
| vb3.post | optimize | status | OK |
+----------+----------+----------+----------+
1 row in set (1 min 21.15 sec)

mmm same problem whit server load...
Treads: 112,110, Post: 1,745,876, Members: 29,111

First day work fine whit 400 users online, second day server go to 8...11.11!!!!!!

i have to uninstall...some fix?

It's great, mysql load average goes as down as it can ;-) Thanks.

I've installed this!

It's working well... I'll look over the server loads over the next few days and report on it.

Overall, took me only 3 hours... most of the time it was trying to find out why I couldn't add a fulltext index to post, to find out that my secured tmp directory was too small, so I had to modify my.cnf to change the tmpdir temporarily. :)

Sorry for disappearing :)
Returning to discussion about SQL requests with or without LEFT JOIN :)
I recently had a chance to do a lot of tests on one large programming forum with about 900.000 posts. And yes - it is true that excluding some forums from searches do not make search run faster... But including left join don't make it perceptible slower :)
But after removing revelance it runs up to 10 times faster!
Here are results as requests and time in seconds below. Each request was executed 10 times with clearing DB cache after each. Fastest and slowest time below. Forums were not closed at that moment and there were about 120 online users. Think that numbers too different because of it :)

Well, my current server loads seem a bit lower than before I installed the hack. But it's not peak time yet. Search appears to be noticeably faster.

John, just tell me which code to use that is the fastest and puts the least amount of stress on the server, and I'll use it. :) Do I just remove the RELEVANCE part in search.php?

yes :) to remove revelance replace

with

and remove string
:)

Thanks again JohnWoo...just modify that in my file....in a few days will see :D