I'm still unclear as to how the old URLs are redirected. Is there a table that holds the redirect information? For example each row in the table has an old URL and new URL. If an incoming link is not found it searches this table and redirects if the old URL is found.
So my assumption was correct, there will be a table that will be used to store the old IDs and the corresponding new IDs. Is it safe to assume that if my forum has 100,000 threads, the lookup table would have to have 100,000 rows?