I have been going through and doing some housekeeping on our solution. I found lots of fields that are indexed that don't need to be. We have 20 copies of this file in production, so I didn't want to open each one and repeat the steps.
I did however make the changes on one file, then use the data migration tool to effectively change the schema.
Interesting thing happened -- the indexes that existed in the old data file, but NOT in the new one - get logged as being rebuilt - but don't seem to exist.
From the migration log:
-- Rebuilt the following indexes --
Target field "TagNum"
From the finished migrated file
Ctrl + i in the field on the source data file has the field indexed and pulls up the list of values.
So I'm not sure if it is actually building indexes, or just logging them or building them and then dropping them?
The file went from 509mb to 535mb upon migration - with 0 new indexes added.