You may get to the point where you have performed a number of migrations with the Data Migration Manager (DMM) - test and/or production.
You may have experienced that a bulk deletion or import gets longer with each migration as your total data in the MSCRM_MIGRATION database (which is either going to be in the SQL Database you specified during the install of DMM or on a local SQL Express instance) increases.
You may also have experienced a small inconvenience where all your migrations have to have a unique name.
All that is needed to get around this small problem is flushing ouu the ImportBase table in the MSCRM_MIGRATION database.
USE MSCRM_MIGRATION; DELETE FROM ImportBase;
