Question - What Happens If A Unique Index Is Set To Bad?
Answer -
If a UNIQUE index is set to BAD, the corresponding table is set to READ ONLY. This lock is necessary since the UNIQUE option of the index can no longer be ensured for each additional write operation that concerns this index in the table. At the latest when the database is started the next time, UNIQUE indexes that are set to BAD are automatically recreated.
As of Version 7. 8, the DBM command auto_recreate_bad_index is available. You can use this command to activate the automatic recreation of indexes (including UNIQUE indexes).