storage gas refund, is gas only refunded when storage is completely deleted? What if a key / value in a mapping is deleted?

Question

I have a which tracks ids for some structs for different users.

mapping (address => uint[]) usersStuff

This mapping for each user can grow or shrink.

If it happens to shrink to 0 for a single user (i.e. with delete usersStuff[msg.sender] ) but the actual variable hasn't been deleted because usersStuff has data for other users, is there a gas refund?

Answer 1

Yes, deleting a mapping entry results in a gas refund.