Question: Each KV pair has 2 copies in arena?

[azuredream]

I'm a C++ beginner, please correct me if I was wrong.
Is it possible to save a pointer to Key rather than a Key object in node?

First copy:
MemTable::Add(): char* buf = arena_.Allocate(encoded_len);

Second copy:
template <typename Key, class Comparator>
struct SkipList<Key, Comparator>::Node {
explicit Node(const Key& k) : key(k) {}

Key const key;
...
}