select on tuple in mnesia

[Rapsey]

If I have a tuple saved in an indexed field in mnesia, something like this:
-record(mnesia_record,{key,val})
#mnesia_record{key = {atom1,something}, val = "blabla"}

Will select call for all keys that are of the {atom1,_} pattern use an
index, or will it have to scan the whole table?


thank you,
Sergej