How do you handle errors? Exception handlers?

The errors can be handled in different way, will list few of the methods which we can achieve via ETL

If it is a critical fact table (Merchandise, location and time (weekly)) then

Non-Critical Data - Foreign Key failure on item, those data can be deviate to a file or table (If we are using the table then we have to model the table in such a way that it can accommodate n number of foreign key data) and process it separately.

Critical Data - Foreign key failure is happened, there should be a process to get the unique foreign key and insert the missing records into the merchandise dimension table with a dummy value and then we should process the fact data immediately.