@jonhattan, you're right about destid not being used much but I thought I sho...

@jonhattan, you're right about destid not being used much but I thought I should put it in for completeness. Our main concern here is joins during migration and I don't think destid is useful there at all. We could consider dropping it from indexes.

@heddn, I think that test is not really checking for efficiency of indexes but to see if they are just present. The existing definition just creates one of sourceid and destid columns and that is why there is only one column in the index each. Are you saying we should add more columns to the map and index? We could do that but is there a benefit there?