Removing broken migrations

[psztoch]

It may happen many times that a version with a damaged migration will be released.
If we improve the migration, on a few systems we may have a conflict with an incompatible md5 checksum - this is sometimes normal.
But it is also very tedious.

What do you think that if a situation such as a checksum mismatch is detected, the <bad_md5> .cancel.descr.sql file is searched and run, which will automatically roll back such a damaged migration.
If the file is not found, a migration error will occur as now and the migration will be aborted.

[rickbergfalk]

I don't really have much of an opinion on how to deal with this issue. I personally don't use the checksum functionality.

Then again I also treat migrations as immutable. If a change needs to happen its always written as another up/do migration, and I don't really bother with the down/undo scripts.