First benefits from performance optimization: I have discovered  “the mother of all queries” in phpBB.

I am not sure about the newest version but the installation I use in diorama contains a lot of queries like:

  SELECT m.word_id

  FROM phpbb_search_wordmatch m, phpbb_search_wordlist w

  WHERE w.word_text IN ('S', 'S', 'S', 'S', 'S', 'S', 'S', 'S', 'S', 'S', 'S', 'S', 'S')

  AND m.word_id = w.word_id

  GROUP BY m.word_id

  HAVING COUNT(m.word_id) > N

These queries belong to the forum search logic and floods MySQL query logs up to 90%. The good news is you can get rid of this logic without any significant functional loss according to this discussion.

To do this just disable “remove_common” function in includes/functions_search.php (e.g. by putting a return-statement in the first line of it).

Already checked this. Works good. Works faster.