With the addition of Bugzilla::DB::Schema and the bz_schema table, it's important that the bz_schema table and the real on-disk schema stay the same. However, sometimes people want to modify the schema locally. Also, there's a chance that the Schema object could get out-of-sync with the local database, and then the end-user would need some tool that we could instruct them to use to fix stuff. So the tool needs to be able to: (1) Modify the existing Schema, keeping the on-disk schema in sync with the Schema object. (2) Do modifications that *only* modify the disk. (3) Do modifications that *only* affect the Schema object. The last two should not be normal functions, but should be accessed only by users who are instructed to do things by a Bugzilla developer or professional consultant. They should also be rarely necessary, except in cases of bugs in the Schema upgrade code.