Imagine this scenario, you are deleting a large number of contacts and you process aborts somewhere during the process. If you are using default parameters in process IFB, you can be in a lot of trouble. Why? EIM have this 3 parameters
COMMIT EACH PASS = TRUEwhith this defaults, this means that after deleting a table a commit is performed. And no rollback is performed. this can leave you with "orphan" records.
COMMIT EACH TABLE = TRUE
ROLLBACK ON ERROR = FALSE
To avoid this, just change your parameters to
COMMIT EACH PASS = FALSEThis ensures that EIM will either complete sucessfully or rollback the batch.
COMMIT EACH TABLE = FALSE
ROLLBACK ON ERROR = TRUE
Just one note, be sure that your database resources are large enough to handle this transaction.