I need an array or list or hash table that will allow me to have keys that are not unique, for example:

"table_name1", "error in field name"
"table_name2", "error in field address"
"table_name2", "error in field zipcode"
"table_name2", "error in field other"

etc.. there will be multiple keys but they could have the same names. Another issue is I could be storing up to 1,000,000+ elements so performance is an issue. Any ideas what data structure I can use?