Backing out a Core Data migration?

I have an app with a very large Core Data database. I have versioned it many times over the past year.

The last time I versioned the database I made one simple change to an entity: I added a new optional attribute. For some reason it would not migrate using Light-weight Migration. I found out much later that this was due to a bug in Apple's Light-weight Migration code resulting from the 'renaming identifiers' that I had needed back in another versioning.

Anyway, I digress...

Because of the bug that kept me from using Light-weight migration, I created a mapping file to help with the migration, not understanding that this would was a much heavier process and would force my users to wait while the app loaded the entire database into memory while doing the migration. It turns out that this is not really an option at all with very large databases and many of my users were unable to migrate the database at all due to memory problems, etc.

So now I want to re-release my app and clear up this problem. The trouble is, some of my users have a database that is somehow marked as being 'in the middle of migrating'. Even with my new code, which gets rid of the mapping file and supports Light-weight migration, users that are in this state, 'in the middle of a migration', don't seem to get reset.

What are my options for backing out a migration? - I can detect that I am in this state because there is a '.myDB.sqlite.migrationdestination_41b5a6b5c6e848c462a8480cd24caef3' file in the Documents directory. Deleting this file does not clear up the migration. My guess is that the database is somehow flagged as being in this state, or is already partially migrated. - I can detect this state and then delete the database altogether. But t开发者_如何学运维his forces my users to re-download their data.

Any Thoughts?

Thanks for you help.

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The only thing that occurs to me would be crack open the SQL store of an affected file and look for flags or something else that might signal the db being in a transitory state. You might be able to write directly to the file and alter something.

That's really ugly problem.