The RTMediaMigration has some code that makes large sites (500+ sites, 500+ media items, etc) come to a crawl. The worst part is all of the media (and how much done) is recalculated on each page load in functions like
get_done_count(). I think that other than the database update code, there should be no migration code running outside of the
RTMedia > Migration screen.
The problematic code is in
RTMedia::update_db(), which instantiates
RTMediaMigration class (and the __construct() function) just to get access to
bmp_table public variable.