Delete element in the middle of mapping

Question

I need to delete an item in the middle of the Everscale solidity mapping containing struct:

struct Example {
    string data;
    uint64 validFrom;
    uint64 valiUntil;
}

mapping(uint64 => Example) example;

example[1668161798] = Example("Start", 1668161798, 1668162798);
...
example[1668163798] = Example("Middle", 1668163798, 1668164798);  //  <-- Need to delete this one
...
example[1668165798] = Example("End", 1668165798, 1668166798);

Question 1

What is the best way to do this in terms of:

1. Gas consumption?
2. Storage?

Is it using the delete instruction work from the Ethereum example, or is it better to rebuild and reassign the mapping?

delete example[1668163798];

Question 2

What happens to the data contained in the mapping's item after using delete? Is there any garbage collector that wipes them out to minimize the storage?

What will happen if I reassign new data on the same index after deletion?

Answer 1

delete example[1668163798];

is the right way to do it. "delete" assigns the default value of the type for the variable it is applied to. For the mapping key, it removes the pair from the dictionary, thus freeing the storage space.

assigning a new value to the previously deleted key is no different from adding any other (key, value) pair to the dictionary; it works just fine.