I'm importing a few tens of thousands of topics with something like 1.3 million posts into ubb7, and it gets really slow as I get upwards of 30k topics. It looks to me like this is because sorting on b_number and using a LIMIT n, 21 to get the next block of 20 topics requires MySQL to filter and sort the entire list of n-1 topics to get to the nth one.
Wouldn't it be faster to pass the last-processed topic number instead of ordinal, and change the query to something like:
select * from ${PREFIX}Posts WHERE B_Topic = 1 AND B_Number > [the last one processed] ORDER BY B_Number ASC LIMIT 20
That runs very much faster on my test system.
Thanks,
-D
